RESEARCH PROPOSAL
COMPUTER LABORATORY FOR CLINICAL DECISION-MAKING

G.A. GORRY
MARCH 25, 1974
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Introduction
As Schwartz hae noted {1}:

“Many discussions during the past decade have considered the use of
computers as an adjunct to medicine. Feu, however, have fully explored
the possibility that the computer as an intellectual too! can reshape
the present system of health care, fundamentally alter the role of the
physician, and profoundly change the nature of medical manpower
recruitment and medical education -- in short, the possibility that the

health-care system by the year 2888 will be basically different from
what it is today.

"Much has, of course, already been said about the role of the
computer in improving the efficiency of the health-care system. These
now familiar projections envision the computer performing a wide variety
of functions such as the scheduling of hospital admissions, the keeping
of medical records and the operation of laboratory and pharmacy. Such
developments in the area of “house-keeping" activities offer
considerable hope for the improvement of both hospital and outpatient
operations but do not come to grips with the more fundamental problems
of the health-care system -- the increasing shortage of physician
manpower and the geographic maldistribution resulting from the
reluctance of today’s doctor to practice in rural or depressed urban
communi ties. Even tess do they give hope of dealing with the difficult
challenge of maintaining a high level of physician competence in the
face of a continued expansion of medical knowledge that tends to widen
progressively the gap between what a doctor should know and what he can
retain and utilize. The computer thus remains (in the light of
conventional projections) as an adjunct to the present system, serving a
palliative function but not really solving the major problems inherent
In that system. There is, in fact, little reason to believe that any of
the current proposala for solving these problems, technologic or other,
will do more than mitigate their severity".

One radical and intriguing possibility for improving the efficiency

and effectiveness of the health care system is to use the computer as an
“intellectual" or “deductive” instrument -- a consultant that is built
into the very structure of the health care system and augments the
abilities of physicians and paramedical personnel. Clearty, however,
considerable intellectual and technological resources must be marshalled

and a long term research commitment must be made if this possibility is
to be realized.

We will argue inthe body of this proposal, that the
principal impediment to the realization of this exciting
prospect is the lack of a good theory of clinical cognition.
Despite successes in certain areas of clinical medicine, no
theory of clinical decision-making has been developed which
can explain the richness of the problem-solving behavior of

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experts: Further, we will argue that the computer is the
key.to the development: of such a: theory: The. computer
provides: an environment in:which: ideas: about process can be
expressed in- a:. quite natural way. Such environment. is:
essential if we-are to advance our understanding of clinical
cognition...

Although. the: idea: of using computers: and: computer: programe: in: the
devel opment: of* cogni tive: theories” is:not mew: {2}, recent devel opmerrts” in
computer sciences amd’ technology make- this idea:more power ful. We have
organized a. team: of computer scientists and medical scientists ina
concerted attack on the problem of understanding. clinical .decision-
making in new and. profound ways. The-Computer: Laboratory concept is one
Which fits-well inte our current activitiess. and indeed, it offers us
real leverage with respect to the growth of: our-efforte. |

What We Propose:To Oo-

Various approaches to the: ‘problems of automating processes. for
clinical decision-making: have: beer: employed by: researchers: in the field;
and considerabte success has been achieved:. We believe that an expert
program: which: cam: deliver~ advice. and: consultatior with respect to
serious clinicat- problems wil! make use of many of these approaches. At
present, however; none of these approaches -is-sufficiently.powerful to
offer the integrative: or administrative capability.required: ta: organize
the: variety: of: problem: solving: approaches: necessary. for: the- full range
of clinical problems.. Thus:while- other researchers continue with the
development. and:refinement: of existing. techniques; we: propase: to devote
our efforts: to: the: problem. of defining and: implementing the: framework
Within which these: techniques: can be organized. and:contro! led...

The onty. examples we. have of the integrative-abilities: which are
required come: from the: performance of clinical experts. Clearly. they
possess: the: administrative: problem-solving knowledge. to shift from one
approach to another as the case merits. For: this reason, the principal

focus. of our efforts.will. be on gaining a~ better: understanding of the
behavior of experts.

We propose to undertake a.program of research which will result in a
new and.significantiy better theory of clinical cognition, with special
emphasis on thes administrative aspects of the-problem=-solving: behavior.
The computer will play. a central role in the formulation and testing of
this theory. Further; because the: concepts upon which the theory will

 

be based will be:expressed in a form which. is programmable, we will have
a new technological framework within which efforts to create
distributable expertise can proceed in concert. This in turn will speed

the realization: of that revolutionary role: of the computer in the
health-care system suggested above.

The activities of the Laboratory initially will be centered on several!
specific research projects which are related to our overal| goal. These
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projects are discussed in detail in the body of this request. Here we
will simply mention them and their relation to our primary goal.

1) Taking the Present 1|1!ness

The present illness is the initial point of contact between the
patient and the physician, and for this reason, it represents a
logical starting point. More importantly, however, the cognitive
demands of taking the present iliness, establishing the facts,
drawing inferences about the facts and about the patient, dealing
with discrepant information and uncer tainty,. etc. are central to
all clinical decision-making.

One of our major projects will be to develop a computer simulation
of an expert taking the present il Iness. Such a simulation will be
‘based on specific mechanisms for solving the various cognitive
problems involved. These mechanisms, in turn, will be central to a
variety of other decision-making programs. The knowledge gained from
this effort and the results of the next project discussed will altow

us to attack the problems of differential diagnosis and the
risk/benefit analysis of management.

2) The Formalization of Clinical Knowledge

A second major project of the Laboratory will involve the
development of new ways to formalize medical knowledge. Initially,
this knowledge will be primarily that which appears in texts or

journal articies on clinical problems, augmented and refined by
clinical experts. -

The criteria by which proposed representations of this knowledge
will be judged includes

a) clarity

b) parsimony

c)} completeness

d) capacity for expressing relations among "pieces" of knowledge
e) the ease with which it can be assimilated by a computer

Loosely speaking, the present iliness project can be said to be
concerned with how knowledge is used, whereas this project is
concerned with formalizing what knowledge is required.

The result of this effort will bea methodology for building a
knowledge base for programs such as the cognitive simulation of the
present iliness, and it should be viewed as being intimately
connected with that project. Further it should provide a basis for
research on the construction of diagnostic and management programs
for various problems by providing a framework within which the basic
knowledge required can be organized. The Laboratory will also
develop programs for diagnosis and management when a good base of
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understanding has been achieved.
3) Model-Based Decision-Making

There are a number of important areas of clinical medicine in
which a .formal ( generally mathematical) model is available upon
which certain diagnostic or management decisions could conceivably be
based. In many of these cases, however, the mode! in question is of
little clinical use. Although the model often surpasses the ability
of even the best physician to deal with certain aspects of the
problem, or with "classic" cases, it cannot cope with a variety of
patient-specific factors which should be factored into the decisions,
or certain emergency conditions which should cause a re-ordering of
the priorities in the model. In general physicians understand how to
alter and refine their approach to a problem in the light of such
factors, but computer programs unfortunately remain very rigid in
this regard.

If we took te the day when various models and techniques are
combined in a single system, it is clear the new flexibility must be
built into the component pieces so that they can be "tailored" to fit
a certain situation, and so that component pieces work coherently
under the same assumptions about the patient.

To achieve this aim, we need new ways to combine medical “common
sense" with mathematical models. The models themselves must be
represented in such a way as to allow this common sense to be
applied. Hence it must be clear to some supervisory program what the
basis for a particular model is, and how changes in assumptions about
the patient affect, this basis, and hence the model.

We will begin to investigate these problems in the context of a
model for the administration of digitalis/digoxin. This problem is a
good one, because the "best" strategy for any patient depends in part
on the use of a model, and in part ona basic understanding the
medical prablems of the patient.

Some Ascurrent Problems

There are several problems which arise in almost all phases of clinical
decision-making, and these will be the focus of a continuing research
activity of the Laboratory. We mention them separately here, but we

want to emphasize that they really represent threads which run through
al! our work.
Privi — G. A. Corr

4) Dealing with Discrepant Information

One of the important problems in clinical medicine is the amount of
discrepant information which must be dealt with. Some of this
difficulty arises because patients are not always accurate observers of
their symptoms, or because they wish to conceal facts from the
physician. Other problems arise from errors in laboratory tests or
medical records. In addition tnere are many problems in which the
discrepancy is not. absolute, but rather relative to some currently
believed hypothesis about the patient.

The question of belief is thus central to clinical decision-making.

We plan to study this problem ina variety of contexts, with the
intention of answering such questions as:

Hou is the credibility of a piece of information established?
How are potential discrepancies among facts detected?
How are conflicts between facts resolved?

What strategies are employed to resolve ambiguities or
discrepancies?

S) The Representation of Time

Time plays a key role in clinica! medicine. Diseases and their
manifestations evolve through time. The interpretation of facts is
often affected by the place of these facts in time. Often time-based
relationships are crucial in making diagnoses or management decisions.

If we are to capture clinical expertise in a machine, we must equip
the machine with an understanding of time and events which take place in
time. Thus the machine needs a minimal ability to place events and
intervals on some form of “time-line”, and to make appropriate
deductions about this arrangement. But much more is required. For
example, we must develop ways to capture the concept of episodes. The
machine needs to understand such fragments as “the gradua! onset of the
disease" and "an abrupt cessation of symptoms".

This is an area where substantive progress can probably be of direct
use to other researchers in the field who to date have employed rather
ad hoc methods to solve the problems of time representation or who have
had to skirt the issue entirely to the detriment of their efforts.

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6) Inquiry and Explanation
Another area in which we will be working is the development of

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mechanisms which allow a user to employ a natural and direct mode of.

interaction with a program and will allow a program the ability to

explain its. behavior in terms which are readily understandable to a
clinician. .

To a large extent, we will rely on research and development of
natural language capabilities by others, in particular some of our

colleagues at 4.1.7, but we will play an active role in adapting their
work to the medical context.

We will play a more central role in the development of the technology
Which will allow a program. to generate explanations. Such explanations
may be based on a variety of principles such as the use of physiological

models. The point is that such a capability must be developed to meet
several needs:

a) the need for users to understand the basis for a program’s
advice, particularly when the clinical problem is a serious one.
b) the need for clinicians working in our group to have access to
facts and procedures used by the program in arriving ata
particular conc!usion.

c) the need for students to interrogate the program to learn
about ite strategies

Here again, progress in the development of these facilities, coup!ed
with progress on our other projects should have an immediate and direct
‘impact on the work of other researchers in the field, as well as a
longer term impact on the delivery of health care.

Summary

In summary, we are Proposing some projects which we believe will
Provide the proper direction for the Laboratory. The problems addressed
by these projects are all basic problems for computer-aided clinical
decision-making. Our emphasis on the study of clinical experts and on
the use of the latest concepts of computer science to express the

results of this study will provide a unifying theme for members of the
Laboratory.

We have already formed a group of computer scientists, clinicians, and
graduate students, which has begun work on these problems. The
Laboratory would greatiy facilitate and accelerate collaborative efforts
of this kind, and it would be a link between the impressive computer
science resources of M.I.T. andthe equally impressive clinical
resources of the Tufts-New England Medical Center. It would also
provide a center into which researchers from other institutions could be
drawn. In all, we envision that the Laboratory would be the center of
new, vital, and important combinations of research and education. Its
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activities should have a significant impact on the computer-aided
delivery of health care, as well as on medical education.

Background

The Laboratory we are proposing here will bring together experts from
the computer sciences and from medicine for the purpose of gaining a neu
and deep understanding of the processes of clinical cognition and
developing the mechanisms to transiate this under standing into
improvements in health care delivery. Here we want to ‘give a brief
history of the development of the research group,. and then because of
our involvment in both medicine and computer science, we want to briefly
review important concepts and developments in both computer-aided
clinical decision-making and in the relation of computer science to
psychology and to theories of problem-solving.

The Development of Our Research Group

In order to put our application into perspective, we want to include
a brief history of the development of the research group.

The nucleus of the group was formed several years ago, and it
consisted of Ors. Schwartz and Kassirer and Professor Gorry. Schwartz
and Kassirer had been working on the problem of encoding the protocols
of experts in computer programs, and had developed a program for acid-
base problems {1}. Gorry had developed a program which used statistical
decision theory to solve diagnostic problems {3}. Because of the common

interest in automating processes for clinical decision-making, the three
joined forces.

The initial efforts of the group were directed along the lines
suggested by the decision theory program. The work was considerably
deepened and expanded during the two years following the initial
formation of the group. A series of papers describing the work were
published, most notably two recent articles ({4 } and {S}). These two
papers consider in detail the application of decision analysis to
Clinical decision making, both insofar as the automation of the process

is concerned, and with respect to the use of this formalism by
clinicians.

Dr. Pauker joined the group in 1971, bringing to it a rare
combination of expertise both in medicine and in computer science.

During the latter stages of our work on decision analysis, we began
to see certain difficulties in using decision analysis as the sole basis

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for a system to deal with real problems of crisis medicine. After.

further definition of these difficulties, we were given a research grant
from HISMA under which we explored these problems. From this

exploration emerged a recognition of the need for a close cooperation
with skilled computer scientists.
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In order to promote a closer union between researchers in computer
science and the workers in our group, we held fast summer a week long
conference on the problems of clinical decision-making and the relevance
of advances in computer science to these problems. Attending the
conference were five members of the M.I.T. computer science faculty
(including Professor Marvin Minsky, the director, of the Artificial
Intelligence: Laboratory. and Professor Edward: Fredicin,. Director of |
Project MAC): and’ the members’ of our group: already mentioned. The major
result. of thie conference was the recognition of the potential benefits
to medicine of a strong. computer science supported research program, and

the complementary benefit to computer science of a close involvment in
medicine.

At this meeting, we resalved to organize a research program which
would bring together first rate computer scientists and clinicians in a
coordinated study of the problems of clinical decision-making. This

proposal and the: work upon which it is based is the result of that
collaboration.

Since that meeting, we have been actively pursuing research in this
area. We have: funded. our activities through small! amounts: of money from
various sources; Despite this limitation of resources, however,. we are
proceeding at arapid rate. In addition to the research discussed in
this proposal, we are attracting graduate students in computer science.
Five graduate: students: are already working. with us, and we would have
more. if more: funds were available.

Professor Gorry has joined the faculty of the Electrical Engineer ing
Department at.M.1.T. and is-working at Project MAC. Professor Sussman
of the Artificial Intelligence Laboratory is: taking an active role’ in
our research efforts, and other faculty, notably. Professors Fredkin and
Minsky are advising us and encouraging our efforts. Most. notably, Or.
Schwartz will. be a Visiting Professor at M.1I.T. next year where he can
devoted increased energy to the research program.

All this causes us to be very optimistic about our ability to mount
an excellent program of research and education in computer science and
medicine. The critical problem now is not the people or the ideas, but
simply. that we. lack funds. Because our work seems so well in line with

the intention of the Computer Laboratory Program, we hope to obtain the
needed funds from that program.
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Previous Research on Clinical Decision-Making by Computer

Broadiy speaking, work on computer-aided clinical decision-making falls
into two categories. In the first category are efforts to develop
computer-based mechanisms for assuring orderiy and complete acquisition
of data concerning the patient. Examples of such efforts are Weed's
problem-oriented approach {6} and work in history-taking, physical
examination , and laboratory testing procedures (See, for example {7}.)
It is believed that with improvements in the data acquisition and data
structuring processes wil! come improvements in either the effectiveness
or the efficiency of the clinical decision-making process, and in
general, this belief seems wel !-founded. ,

In the second category fall al! the efforts which are directed at
developing computer realizations of procedures for making diagnostic
and/or management decisions. In general, activities of this type have
paid fess attention to the orderly acquisition of facts than to the
problems of interpreting the facts as presented. Within this category,
however, a further division of efforts can be made. This division is
based on the view which the researchers take of the decision-making
procedures they are developing -- whether these are thought to be
descriptive or normative. In the former case, the researchers have
attempted to codify the way in which experts actually make diagnostic or
therapeutic decisions. In most cases, the determination of exactly how
an expert behaves has been rather ad hoc, involving a mix of
introspection, interview, and various forms of observation. Some
notable successes have been achieved in this way. {8} (Here we are
measuring success in terms of providing distributable expertise about
some problem domain.)

Those workers with a more normative bent have emphasized the
development of models and procedures for decision-making which are
thought (funder certain assumptions) to be the basis for optimal
decisions. In almost al! cases, the assumptions are met only loosely,
and no real claim of optimality can be made. Still, the general flavor
of the work suggests that computers ought to make decisions in this way,
Without regard to the way in which humans make the same decisions. The

more normative approach has also yielded success in certain areas
(e.g, {3}, {5S}, and {9}) ,

Aithough work in both of these categories has shown considerable
promise, and research continues actively on both approaches, no program
has been produced which can cope with the real complexities of the
clinical situation, e.g. time dependent changes in disease, multiple
disease in the same patient, and a variety of patient specific. factors
Which have an influence on both diagnostic and management strategies.
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We believe that these approaches and the techniques which
they have produced will enter into.an expert system in an
important way. We do not belicve, however, that either of
these approaches, as currently employed, can be the basis of
the kind of administrative and integrative structure
required in such an expert system.

For this reason, we want to explore in some detail the methodological
limitations of the approaches which have been used to date. It should
be remembered that our criticisms of these approaches are in the context
of trying to provide an overall framework for clinical decision-making.

1) Elow Charting

The ‘descriptive’ approach is to construct a flow chart to
represent the way in which a particular problem is to be handled {e.g.,
{7}, (89). As was noted above, the manner in which the flow chart is
obtained is usually ad hoc. Sometimes the flow chart represents the
opinion of an expert as to the process he believes he uses. In other
cases, it is based on a mixture of introspection and more formal
modeling of aspects of physiology or pathophysiology. In any event, the
resulting flow chart is an encoding of a decision procedure which is

deemed to be a goad one to follow in the particular clinical area in
question.

There are two major difficulties with this approach insofar as complex
clinical problems are concerned. First, a rigid definition of the
logic to be used in a given situation may be tmpossibly cumbersome if it
attempts to account for’.time dependencies , multiple interacting
problems, patient specific constraints, etc. Even if such flow charts
can be constructed for subproblems of a clinical probiem, the decision
as to how and when they should be combined, modified, and applied to a
given situation remains. The representation of knowledge in flow charts
makes this latter decision exceedingly difficult. Medical knowledge
about a given clinical situation is implicit, not explicit in a decision
flow chart. Because the reasons for a particular branching are not
available to the program, in general it cannot make even simple
deductions about them. Thus, unless the clinical situation matches
exactly a series of branches in the flow chart, the program is helpless,
because its lack of underlying knowledge prevents it from adjusting its
approach to a non-standard problem.

Further, with this kind of structure, a user cannot inquire about the
basis for a decision or suggestion from the program. . And, an expert
cannot add new knowledge to the program except through a laborious
search through the programs or frames of the flow chart to ascertain

What the program already knows a given subject, and how the new
knowledge should be related to it.
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2) Decision Analysis:

' Another approach to the problem of computer-aided decision-making
is to give a program an explicit description of the relations between
findings and diseases and between actions and outcomes. Then one can
Incorporate an inference procedure into the program for sequentially
deducing the path it should take with respect to a given problem. This
approach is the basis for the decision analysis program we built for

acute renal failure €{3} and (S}), and has been used by others in
different contexts. (e.g., {9})

By explicitly recognizing the uncertainty in the relationships
and by generating a decision tree for each new situation, a decision
analysis program for balancing costs and benefits can deal with the
equivalent of a very large number of flow charts.

This work has demonstrated that decision analysis is a very power ful

approach to problems of balancing risks and benefits in the clinical
context. — ,

With this approach, however, there are Jimitations which pose very
serious problems: when real-world complexities are introduced. Our
current methods for the explicit description of the probabilistic
relationships, the courses of diseases, action-consequence
relationships, etc. are very rigid and to a large degree, artificial,
and although these forms of description are well-suited for the decision
analysis algorithm, they are very cumbersome for the expression of
medical facts in medical terms. Thus, a time-consuming and error-prone
process must be undertaken to translate descriptive statements (made by
experts, for example) into material which the program can use correctly.

A second problem is that it is very difficult to give procedural
advice to a program based solely on decision analysis. For example, an
expert might want to suggest a logical procedure (perhaps a "flow-
chart") by which a specific situation can be efficiently and effectively
handied. He may have processed (in some way) al! the uncertainties,
risks, and benefits associated with the situation, and he knows that the
procedure is useful. He cannot, however, add the procedure to the
program directly. The options are either to reprogram the system or to
determine some parameters which, when used by the decision analysis
program, cause it to do the “right” thing. Both alternatives are
unsatisfactory if much knowledge is to be added to the program.

Finally, to the extent that explicit descriptions of diseases,
etc., are formulated in terms of probabilities, the knowledge of the
program is basically a mass of numbers, and the explanation of decisions
or suggestions made by the program will be very difficult for an expert
(and more so for the average user) to understand. Concepts and language
naturally employed by the expert to express his knowledge have to be
converted to a set of numbers which when coupled with some decision
produced the same results.
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To summarize, neither the flow chart approach -nor decision
analysis can be the basis fora program which deals with
complex clinical diagnosis and management problems. Both
approaches have value in certain circumstances and should be
used as appropriate, but new techniques are required: for-a
program to be able to deal with the full range of
complexities which arise in serious clinical situations.
Advances are also required if it isto be possible for an
expert to interact witha program in sucha way that the
program can assimilate the expert's knowledge, and fora
user of that program to be able to have natural and direct
‘access to. that ‘portion of the knowledge which is most
relevant to the clinical problem he is considering.

The need for these innovations is underscored by the diversity of

knowledge which experts used. They use descriptive, causal, procedural,
and administrative knowledge along with common sense. It seems apparent
that current formalisms are suited for only one or two types of
knowledge, and -that a new framework for organizing and using these
diverse kinds of knowledge is required. More recent work, such as that
of the Rutgers Special Research Resource on Computers in-Biomedicine is
directed to the solution of some of these problems. We hope that = the

proposed Laboratory would establish close relationships with such
activities.

The Relevance of Advances in Computer Science

Advances in computer technology, including dramatic increases in
information storage capacity and the development of remote access
capabilities tn the form of time-sharing systems, suggest the
possibility mentioned above, that computers would .gerve as a repository
for medical expertise and as a means for disseminating that expertise to
points of need within the population. If such *knowledge-based’ systems
could be built to serve as consultants for clinical problems, they could:
be replicated feither in fact, or effectively through multiple remote
access to one system) as needed.

Unfortunately, this computer power alone is not enough to carry us to
our goal. As we noted in the introduction, the major impediment to
progress is our lack of understanding of the processes of clinical
cognition. Therefore, advances in computer programming and technology,
alone, will not solve the problems. It is important, however, ta
recognize the role which advanced computer science and technology play
in research such as that being proposed here.

It is an unfortunate fact that although advances in computer science
and technology cannot solve the problems, deficiencies in either can
pose a serious hindrance to progress. Until recently, various attempts
to formulate behavioral theories of complex processes would have
suffered from a serious lack in the existing technology, the technology
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i

ae
*

which had to be the testing ground for these theories. As a result, the
development of theories of intelligence in certain domains was retarded.

In recent years, there has emerged from research in computer science
anew *technology’ for representing some kinds of knowledge in computer
systems. This capability is relatively new, dating from the late
196@0’s, and we believe that its availability wil! greatly ameliorate the
problems of formulating and ‘testing cognitive theories. This in turn
Will have a very beneficial effect on research into clinical decision-
making. We are not claiming that there are no technological problems in
our path; on the contrary, there are many. It is our opinion, however,
that this new technology permits us to begin to explore new: forms of
procedures which simulate aspects of clinica! cognition.

The advances and ideas to which we are referring are concerned with
new techniques for programming computers and new techniques for
representing knowledge and meanings in programs. In the old style of
making "computer models’, things were very rigid. In the new style, it
is much easier to include knowledge about. how contingencies and side
conditions affect, not only the states of the models, but especially hou
the modeis are to be applied. in various situations. (Later we will
describe some of our. ongoing research in applying some of these ideas to
the problem of digitalis/digoxin administration.)

In the new style, communication between programs is more flexible and
direct. Some kinds of knowledge can be represented as procedures, able
to intervene actively in the control of other programs whe specified
‘patterns’ arise in the other programs’ operations.

 

Goai-Directed Programming Languages

Rather than being organized as a step-by-step sequence of actions to
be performed, specified in advance by the programmer, programs in these
programming languages are controlled by the activation of certain
statements calied goals. When a goal is activated, the system retrieves
from a data base of knowledge statements those that match the ‘pattern’
of the goal. (A pattern is a description of a state of affairs ina
model, or an encoding of some fact about the world, etc.) These
retrieved statements then serve as advice about what should be done to
achieve the goal; they may dictate that a certain program be run, that
the goal be replaced by one or more subgoals, or that certain priorities

be re-arranged., and then control be returned to an earlier, superior
goal! system. ,
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Understanding Natural Language

For twenty years, the public has been titillated by promises that
computers would understand natural language and even translate from on
language te another. A justifiable skepticism has resulted from such
promises. Although progress in the theory of ‘syntax’, both formal and
informal was steady, this progress did not lead to the anticipated
improvement in the computer’s ability to handle language. The trouble,
of course, is that syntax is not enough. A deeper understanding of the
semantics of language was required. Only in the late 1968’s with the
work of such people as Winograd, Woods and currently Martin, were the
earlier skirmishes with the problems of syntax and semantics sharpened
into serious attacks on the problems of the meaning of !anguage. (See,
for example, {18}.) Thus although real problems remain to be solved,
there is now justifiable optimism that a natural and direct interface
between a user and a knowledge-based system can be bui'!t.

We want to underscore the importance of research on natural language
to the kind of work we are currently doing, and to the proposed work of
the Computer Laboratory. Of course, there is the obvious advantage of
having a natural language interface with a program which contains
clinical knowledge about some domain. Such an interface will permit the
direct involvment of various. experts (some not actively involved with
the research of the Laboratory) with the program. This involvment will
provide invaluable feedback with respect to the facts’ in the program
and with respect to the theories upon which the program is based.

A second benefit, perhaps, is less obvious. It has become clear that in
large part the major impediment to progress in natural language research
has been in semantics rather than syntax. The recent progress has built
on new and better schemes for representing meanings. Further, as this

research progresses, these representational schemes will be further
developed and refined.

Even a cursory study of the kinds of knowledge employed by experts in
solving clinical problems shows how much use is made of conceptual
frameworks which at present are receiving increasing attention § in
language research. Such concepts as time, causality, change, etc.
require deep analysis if machine representations of their meanings are
to be found. The central role that such concepts play in medical —
knowledge means that progress by natural. tanguage researchers wil!
aimost certainly benefit our research directly. In fact much of our
current thinking about representation of medical knowledge is strongly
influenced by our colleagues (e.g. Martin) who are working on English.
Privileged Cone G.A.Gorry FS Page 1S

Recognition and Analusis of Conflicting Goals

 

In many problem-solving applications, the recognition of conflicting
goals is an important problem. Further, once these conflicts are
recognized, it is important to have some means for resolving them. In
earlier problem-solving programs, the recognition of goal conflict was
generally difficult, because the goal structure of a program was
implicit im the program itself. As we noted, the use of goal-directed
programming languages lessens this problem considerably.

The analysis of conflicting goals, although still a significant
problem, is also an area where improvements have been made. . In the
past, conflict between goals was handled by very crude strategies:
either the goals were assigned simple priorities, or a trial-and-error
search procedure would be tried first on one goal and then on the other
in the hope that both would be achieved in some attempt.

Onty recentty have programs been developed which monitor their own
performance sufficiently well to recognize and describe conflicts as
they occur.Such monitoring is made possible in large part by the use of
the goal oriented languages mentioned above to make the intention of a
program more clear. (See, for example, {l1}). Once in the open,
problems of conflict can be faced (perhaps by special purpose programs)
instead of being hidden in the rather arbitrary control structures of
conventional programming systems.

Although we cannot say with any certainty exactly what processes
would be needed for a computer simulation of the clinical cognitive
process, it seems certain the performance monitoring and the analysis of
conflicting goals would play important roles. Therefore advances from
computer science research in this area are undoubtedly important for our
proposed research efforts.

The Role of Computer Science Methodologu

Perhaps the most important contribution which computer science
research can make to the activities of the proposed laboratory is
methodological in nature. The major reason that cognitive psychology
has made relatively little progress with respect to understanding
behaviors as complex as that involved in clinical decision-making is
because there was a serious shortage of ways to describe the more
procedural aspects of that behavior. As has been argued in {12}:

“The community of ideas in the area of computer science
makes a real change inthe range of available concepts.
Before this, we had too feeble a. family of concepts to
support effective theories of intelligence, learning, and
development. Neither the finite-state and stimulus-response
catalogs of the Behaviorists, the hydraulic and economic
analogies of the Freudians, or the holistic insights of the
Gestaltists supplied encugh technical ingredients to develop
Privileged "as C.A.Corry GD Page 16

such an intricate subject. It needs a-substrate of debugged
theories and solutions to related but simpler probtems..
Computer science brought. with it.a flood of such ideas, well:
defined and experimentally - implemented; for thinking. about.-
thinking; only-a fraction of them: have distinguishable
representations in iraditional psychology.

It is this: rich set: of: ideas which> wee phaacto: exptotit: ine the:
description and: analysis-of ctinical ‘cognition. From this effort-wi ll
come a new. theory.of the behavior of clinicad experts.andinew concepts.
for the realization: of this. behavior in a computer.
Privileged Con aD G.A.Corry _ Page 17

’

Research Pian :

introduction

In order to provide a context for our discussion of the research plan
for the Laboratory, we want to re-iterate our goals, and to relate these
goals to our perceptions of the needs of the health care system.

We propose that the major activity of the Laboratory will be
the use of the computer and advanced computer science
methodology in the study of clinical decision-making. From
the activities of the Laboratory will come two major
results: 1) a@ deeper and better-articulated theory of
expert clinical cognition, and 2) mechanisms for realizing

the concepts of the new theory in computer programs for
clinical decision-making.

The reasoning undertying the organization of the Laboratory around
these themes is as fo! lous. We start from the premise that there is a
need for distributable expertise concerning a number of clinical
problems. Our particular interest is in the domain of serious medical!
problems, problems which are often potential ly life-threatening. If we
can make progress in understanding the way in which serious and complex
problems should be dealt with by a clinician, and hence by a computer,
we will be able to develop new technology of considerably improved
flexibitity and power which will be applicable across a broad range of
medical decision-making applications. It can be anticipated, for
example, that these advances will have an impact on the ability of the
practicing physician to deal with complex or serious medica! problems,
placing the consultant as near as the nearest console. Such expertise
should make far more effective the performance of allied health
personnel, such as nurse practitioners and MEDEX personnel. In remote
rural areas, for example, the availability of expert consultation should
make it possible for allied professionals to deal competently with
problems more serious than they otherwise could care for. In addition,
the computer should be able to serve an important triage function,
assisting the non-physician in his decisions concerning referral - in

effect telling him when he should transfer the patient to a physician
for care.

At present, however, the techniques for providing computer-based
consul tation are limited in application and remain generally
incompatible with one another because no mechanisms for organizing and
integrating them in a more general clinical context.

It is this lack of integrative mechanisms which is one of
the principal impediments to the realization of the full
potential of the computer in health care delivery.
Privileged ConQepreeeaas, G.A.Corry Gi - Page 18

Qur goal is to undertake the research which will produce these
integrative mechanisms, and to do this, we have turned to the study of
the behavior of clitnical experts, because these experts have

demonstrated their abilities to combine various approaches into a
coherent strategy suitable. to a given § situation. We should begin by
understanding hon they achieve their performance. Recent advances in
computer science provide us with new building blocks from which we can
construct a better theory of clinical cognition. This theory will be
developed through extensive use of computers and computer programs as a
medium for expressing the theory, and as tne means by which the theory
is tested.

Below we will outline a set of research projects which we believe have
the proper orientation to yield major progress toward the understanding
we are seeking. As our work progresses, of course, new paths will
become apparent, and our ability to define probleme more sharply will
increase.

In what follows, we have listed the principal participants in each
project. ‘Each group of principal participants contains computer
scientists and clinicians, and the activities of the groups are fully
collaborative. In areal sense, everyone mentioned in any project has
an active interest in all the projects, but we thought it might be of
some interest tp the readers of this proposal to know who currently
plays a major role in each project.
Privileged coMeiieanamas C.A. Corry Page 19

Taking The Present Iliness

Principals ;
Professor. G. Anthony Gorry
Peter 8. Miller

Or. Stephen G. Pauker

Or. Wiltiam B. Schwartz

"Will, as Schwartz has suggested, the computing science “largely replace
the intellectual functions of the physicians?". I think not. The
subtie process of the patient-physician interaction and the input we
receive from this interaction has not yet been reduced to precise

mathematical terms. Attempt as we will to analyze this subtle process,
it appears that {despite} our best efforts to penetrate {it!, this
mystery will elude us for some time.’

{Warren Glaser, Professor of Medicine, in a comment on a
forthcoming article on computer-aided diagnosis}

The sentiment expressed in this quotation is shared by many physicians.
Those who have thought carefully about the interaction between a patient
and a physician realize the complexity of the behavior involved. When a
physician is confronted with a patient with one or more presenting
problems, he enters into a mode of data acquisition and problem solving

known as ‘taking the present illness’. This activity is one in which
virtually allo clinicians participate every day. When we try to
understand this process in detail, however, we find that it assumes a
very complex and often subtle character. In fact, virtually all the

problems of clinical cognition arise in this context. The process is
like a puzzle for which some of the pieces can be rather easily found
and described, but for which others remain quite vague and apparently
ili-formed, while some appear to be missing entirely. | The question of
interest here is to what extent can we identify the pieces of that
puzzle and put them together to form some coherent picture.

Qn the other hand, if a machine is to understand the process of
clinical problem-solving, it must understand the taking of the present
illness, because it is this process which provides much of the
underpinning of the rest of the decision-making activities. Therefore,
a deep understanding of the behavior of the clinician in this setting
would provide a great deal of knowledge about how to support clinical
decision-making. Additionally, we chose to begin work on the present
illness because it represents the initial point of contact between
patient and doctor, and because of the richness it presents with respect
to cognitive processes and the integrative demands it places on the
clinician. Further, it has the advantage that issues of risk and
benefit such as those we addressed in our work on decision analysis can
be ignored. Later, as our understanding increases, we can move the
boundaries our our work to include these issues as nell.
Privileged “Cas C.A.Corru Page 28

Preliminary Work

Our activities began with the analysis of protocols, tape-recorded
records of the verbalized problem-solving behaviors of clinicians.
These protocols are augmented by in-depth questioning of the clinicians
regarding their approach to specific clinical problems and by criticisms
offered by these same clinicians of preliminary computer realizations of
our hypotheses concerning their cognitive processes. The purpose of ail
these efforts is to gain a deeper understanding of the way in which

clinicians actually deal with the complexities of the clinical
environment.

We have devetaped our hypotheses to the point where it has been
possible to implement a rudimentary computer simulation of the process
of taking a present iliness. Though very detailed studies of the
problem solving behavior of that program, we have gained new insights
into the process. The use of the computer as the medium for the
expression of the theory has aided enormous!y the advancement of that
theory. This clase man-machine exploration of the behavior of the
simulation of the theory will be a key aspect of our research "style".
Of course, this style has the additional benefit that when a
satisfactory theory has been developed, a program which takes an

excellent present iliness for the given problem domain will also be
available,

A further aspect of our style has been our emphasis on a “complete"
examination of the issues involved in taking a present iliness for a
single complaint (in this. case, edema). By forcing ourselves. to
consider even “minor” differences between the behavior of the program
and the behavior of the clinician as problems for investigation, we have
considerably sharpened our understanding of the process the doctor uses.

Now we want to present our first, rather rudimentary understanding of

the problems and processes associated with the present illness. Then we
Will describe our first theory and the computer realization of that
theory. Finally we will discuss our research plans for this project.

Observations of the Present Illness

The physician, when taking the present illness, asks the age and the
sex of the patient, and elicits a chief complaint. The latter is the
problem which caused the patient to seek medical attention, but it will
often be closely followed by mention of other problems the patient has.
In fact, one interesting problem which is currently of concern to us is
how a clinician Jinks several presenting problems together. For
simplicity of discussion, however, we will assume that the patient
presents with a single chief complaint.

The response of the physician to the chief complaint will vary in
details, but the principal thrust of it will invariably be at
Privileged C@MEMMMEB © G.A.Gorry uD Page 21
elucidating and refining the description of the complaint as given by
the patient. For example, if the patient’s chief complaint is ’swelling
of the face’, the physician’s questions generally will explore the
duration of the swelling, its specific location (e.g. around the eyes),
the symmetry of the swelling (is it only on one side of the face?), etc.

The character ization of the presenting complaint is impor tant because it
is this characterization which along with the age and sex of the patient

gives the clinician his initial framework or context within which to
work. -

The rapid selection of a context is vital for the
clinician. The clinician is about to hear a reasonably
large amount of information from the patient, and if he is
to be able to organize that information and to deal with it
effectively, he must have a framework into which it can be
fitted. Because of the breadth and diversity of medical
problems and the scope of knowledge concerning these
problems, a failure to focus attention and to narrow
drastically the domain under consideration will prevent the
clinician from understanding what he will be told.

Note that this is the reason physicians require the age and sex of the
patient at the outset of the history; because these facts, in
conjunction with the chief complaint provide a great deal of focus for
what follous. Consider the difference in your reaction to the chief
complaint of ’severe, progressive weakness’ in the case of an 8@ year
old man, and that of a 13 year old girl.

Therefore the initial goal of the physician in taking the present
illness is to get an adequate description of the chief complaint of the

patient. What constitutes an adequate description, however, is
determined by another fundamental goal, namely that of gaining a
framework within which to understand the information which will be

forthcoming from the patient.

In some cases, fragments of this ‘investigation will appear to be a rote
recitation of a standard sequence of questions (e.g. in the case of
abdominal pain, ’Is the pain made worse by lying down?’, °Is it made
worse by eating?’, ‘Is it made better by eating?’, etc.)}. Other
fragments will be strongly influenced by the responses of the patient.
For example, if the swelling of the face is periorbital and symmetric,
the physician might want to know whether it appears in the morning ‘and
disappears during the day. If the answer is yes, then he might well
transfer his attention to an investigation of possible pedal edema. On
the other hand, if the swelling is in one cheek and is. painful, the

investigation might switch to questions of recent dental work on the
patient.

Clearly, then, the path of the investigation of the chief complaint
taken by the physician is in part a function of the responses given by
Privileged mY G.A.Gorry > Page 22

the patient to the former's questions. This path is equally well a
function of the clinical knowledge of the physician. Onty a doctor who

recognizes the periorbital edema described above as very likely the
result of renal disease (specifically acute glomerulanephritis or less
often, nephrotic syndrome} would follow the path suggested. ‘So

underlying the observable behavior of the physician ts a knowledge base,
the use of which is only implicit in the process of investigation.

That the investigation of the chief complaint foltows a path determined
by both the medical {and other) knowledge of the clinician and the
responses and descriptions given by the patient is apparent to anyone
who has looked at the present iliness in even the most cursory manner.
Thus it is non-controversial that these two factors are pieces of our

puzzie. What remains unclear is how these pieces interlock in any given
situation.

The exploration of - the chief complaint generally. results in a much
sharper characterization of it than originally offered by the patient,
although usually only certain additional features of the complaint have
been elicited, i.e., the exploration of the complaint has been stopped
short of exhausting all the properties which this problem might
conceivably have. This of course raises the possibility that some
aspect of the patient’s problem has been overlaoked, and the need for
further investigation may arise in later in the session.

The characterization of the chief complaint as elaborated by this
process can prompt a number of different behaviors on the part of the
physician. In certain cases, the description of the complaint suggests
little to him, and so he may simply encourage the patient to volunteer
more information ("Have you had any other difficulties lately?’) or he
may begin a ‘review of systems’ type of investigation of the system
involved in the patient’s probiem.

If the latter approach is used, however, it will seldom persist as the
basic modus operandi, because it is too passive for use in taking the
present iliness, and it is used here only as a temporizing measure. As
soon as it yields some additional information, the physician will assume
@ more aggressive stance with respect to information gathering.

The purpose of this excursion into the review of systems is the same as
that underlying the original attempt to refine the characterization of
the chief complaint, namely to get just enough information to glean a

good suggestion of a context for further discussion of the patient’s
problems. ,

The initial context chosen will of course be further refined as the
present if tnmess is taken. It may be an organ system (in the sense that
the chief complaint is strongly suggestive of a problem with that organ
system); it may be much more specific in that the chief complaint might
suggest a specific disease. (Of course, there may be more than one
disease or organ system suggested.) In any event, the extent to which
Privileged Cas G.A.Gorry a> Page 23

the clinician pursues the characterization of the chief complaint
depends on the search for an appropriate context and the potential.
availability of contexts which are quite specific. For example, the
facial edema described by the patient above would be pursued to
establish its specific location and temporal pattern because of the
specificity of the renal disease context which would result if the
appropriate characterization could be achieved.

At its most macroscopic level, the taking of the present illness can be
described as the clinician moving from context to context with
occasional returns to previous!y-invoked contexts. At each context, the
activities of the present i!|Iness can be thought of as being under the
control of that context. By this we mean that the questioning of the
patient is directed at either the confirmation of details associated
With the context {such as asking . about pedal edema because it is
generally found when periorbital edema is present) or at the selection
of a more ‘specific’ context (as when the clinician asks a patient with
exertional dyspnea whether he has paroxysmal nocturnal dyspnea in order
to choose between the contexts of lung disease or heart disease).

Present iliness or Diagnosis?

Before we continue our discussion, we want to comment on the role uhich
diagnosis plays in the present iliness. Clearly, the present illness is
*driven’ by the desire to establish an understanding of the patient’s
problems and their interrelations with one anothers hence the clinician
is seeking a diagnosis which is suitable as a basis for management
decisions. There is a very real sense, however, in which the present

illness is more than diagnostic process as the latter is conventionally
construed.

Normally we think of a diagnosis as an inference about the state of the
patient which is based on his signs and symptoms, and we call the
activities associated with the collection of information (identification
Of signs and symptoms) the diagnostic process. We have noted that the
taking of the present itiness is also an information gathering activity,
but it is directed as much toward the problem of ascertaining what the
facts are as it is toward the problem of what the facts mean.

Although we admit that there is a level at which one can view the
present illness as part of the diagnostic process and the process of
diagnosis as an integral part of the taking of the present illness, we
feel that the distinction we have made has some merit. It helps expand
our view of the problems of clinical cognition.

For example, when we think only of ’the diagnostic process’ we tend to
think of such questions as ‘Nhat inferences can you draw concerning a 28
year old man with dyspnea and orthopnea who had an attack of acute
rheumatic fever when he was 15, and... etc.” We tend to view the
problem as understanding the meaning of a constellation of findings as
given. We assume that the patient indeed does have dyspnea and
Privileged quits G.A.Gorry i> Page 24

orthopnea and that the attack of rheumatic fever actually took place.

In taking the present iliness, however, the clinician often is not given
these facts, but must ‘dig them out’, and even then he may be left with
significant doubts concerning the facts themselves. It is this

additional aspect of establishing and characterizing the facts and
assessing their reliability which we are emphasizing in our rather
arbitrary distinction between the process of diagnosis and that of
taking the present iliness.

Now that we have made the point that.the two activities of establishing
the facts and interpreting the facts are central to clinical cognition,
We will mow explore some of the ways in which these tuo activities
interact, and we will drop our distinction between taking the present
illness and working toward a diagnosis.

Prerequisites for Clinical Cognition

Although many of the details of the processes employed by. the clinician
in taking @ present iliness or in praceeding to a further diagnosis are
still obscure, it is possible to identify some major aspects of the
general cognitive process. We can do this by analyzing the task
environment of clinical medicine. A physician who is well adapted to
that environment will necessarily possess cognitive processes for
dealing with each of the major demands placed upon him by the
environment. Although we may not be able at present to give much detai |
concerning these processes, we will have made a first step by
recognizing the necessity of their existence. (In the following
discussion, we make use of some terms borrowed from Minsky {13}.)

1) Expectation and Focusing

The first problem that a clinician faces when he is dealing with a
patient is that both the number of disease states and the number of
possible findings which may have some relevance are extremely large.
This means that the clinician faces a search through a potentially
bewildering maze of possibilities. Because his cognitive capacities are
limited (especially with respect to the number of "simul taneous’ paths
he can explore), he must use the facte as presented te drastically
reduce the number of possibilities which he will consider in any detail.

As we noted in our brief discussion of the present illness, this rapid
focusing serves the principal purpose of providing the clinician with a
context for his further problem solving activities. In our studies of
expert clinical decision-making, we have been struck by the rapidity
With which experts achieve such a framework. When they are presented
With only a few (tuo or three) facts, experts almost always have one. or
two working hypotheses. It may very well be that the hypothesis first
chosen will later be discarded. Our point is not that this first choice
i8 an accurate or optima! one. It is a good working hypothesis,
however, in that it brings important structure to the problem.
Privileged Ras 6.4. Corr Page 25
at Fe

Because the stimuli for this focusing are the presenting signs and
symptoms of the patient, it is reasonable to infer that the expert
remembers patterns of findings which "point to’ good working hypotheses
or contexts for those findings. Our current speculation is that these
patterns contain relatively little detail, and they serve only as a
first rough cut at the problem of classifying the patient. This
speculation is based primarily on the experts’ descriptions of the

patterns they are using and on the rapidity with which this focusing
takes place. -

When a context has been selected, the clinician appears to match the
findings of the patient against amore detailed description -of the
prototypical pattern of findings associated with the context. For
example, "shortness of breath in a S8 year old man’ immediately suggests
the contexts ‘heart disease’ and "lung disease’. (Notice in fact how
focused these contexts are relative to the total number of disease
states which could be presented by the patient.) Most clinicians would
proceed immediately to the characterization’ of the shortness of breath
in order to focus on either heart disease or lung disease.

This attempt to match the presenting findings or the chief complaint to
@ more detailed pattern for a context is typical of the activities which
underlie much of the present iliness. For example, consider the
presenting problem of periorbital edema. It immediately suggests (among
a few other things) acute post-streptococcal glomerulonephritis. A
renal expert would very likely move directly toa series of very
detailed questions concerning the temporal pattern of the edema. The
context of AGN has already been 'suggested’; the detailed examination
of the characteristics of the edema will determine whether this context
will govern the succeeding questions of the clinician.

2) Elaboration

Once a context has been chosen, the clinician faces the problem of
confirming his choice. This confirmation requires tno steps: first, he
must convince himself that the rest of the signs and symptoms presented
by the patient conform to his understanding of the disease state or the
Physiological state represented by the context, and second, he must
assure himself that these findings are not better associated with one
another in some other context.

One of the fundamental principles which we have observed in out
studies is that experts use the principle of parsimony. The expectation

 

that all the patient’s findings are related to the same problem is
strong in the clinician's mind. He yields this idea only grudgingly.
In our discussion below, we will see examples of the major role this
idea plays.

The process of elaboration is very complex, involving several
distinct, but interacting activities. ,