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Special Articles

PAY-OFF, HEURISTICS, AND PATTERNRECOGNITION IN THE DIAGNOSTIC PROCESS

H. A. F. DUDLEYCh.M. Edin., F.R.C.S.E., F.R.A.C.S.

CHAIRMAN, DEPARTMENT OF SURGERY, MONASH UNIVERSITY, ALFRED

HOSPITAL, MELBOURNE, AUSTRALIA

Summary Now that so much attention is being paidto the way in which computers can assist

in diagnosis, it is appropriate that the diagnostic processshould be presented in more formal terms. There seemto be three main methods—pay-off, heuristics, and pat-tern recognition. With pay-off, the emphasis is not somuch on the probability of disease being present as onthe results of treatment: to treat acute appendicitis asmesenteric adenitis would be disastrous, so, when the

diagnosis is uncertain, the best pay-off is achieved byrecommending surgery. Heuristics is a process wherethe ultimate goal is known (for example, to open theabdomen or not), and inquiries are designed with thisgoal in mind. Both heuristics and pay-off lend them-selves to handling by computer. The third approach,pattern recognition, is difficult to analyse since, byanalogy with gestalt psychology, the whole is greaterthan the sum of its parts.

INTRODUCTION

COMPUTERS and their considerable manipulative powerhave rekindled interest in the analysis of the diagnosticprocess, and two recent papers have dealt with bayesianprobability and with the definition of disease.2 Althoughsuch theoretical studies provide essential background,they may obscure some of the more practical aspects ofhow doctors work. Just as the engineer, while acceptingthe full rigour of the mathematical treatment of a pro-blem, may yet use approximations to analyse a practicalissue, so the physician may, while appreciating theformal logic of diagnosis, adopt other techniques or

short-cuts at the bedside.Without attempting to draw too great, and inevitably

too arbitrary, a distinction between the noun " diagnosis "and the operative phrase " diagnostic process " this paperis concerned with the latter, for it seems important toestablish that the doctor uses certain methods whichare capable of investigation and which may contributeas much to our understanding and to the possible appli-cation of computers as does attempted axiomatic analysisof the noun " diagnosis ". There are at least threemethods used informally by the clinician in reaching adiagnosis: all three have been subject to a measure ofmathematical and logical study but as far as I am awaresuch study has not yet been applied to the diagnosis ofdisease in human beings. These methods are pay-off,heuristics, and pattern recognition.

PAY-OFF

In simplest non-mathematical terms pay-off is exactlywhat it means-the positive or negative result in gain orloss which accrues from a particular outcome. Thus,the pay-off for a win on a horse at three-to-one againstis a dividend of three times the stake; if the horse losesthe pay-off is negative, the loss of the stake. At these

1. Hall, G. H. Lancet 1967, ii, 555.2. Scadding, J. G. ibid. p. 877.

odds a negative pay-off is more likely. Particular coursesof action may be contrasted-e.g., to go to war or notto go to war under certain expectancies of your potentialenemy doing the same. Sophisticated manipulation ofalternative policies such as these and of their pay-offhas led to the whole new jargon of nuclear terror.3 Thephrase pay-off in fact has a formal meaning in gamestheory 4 as the computed long-run gain or loss achievedby a participant playing alternative strategies againstan opponent who has the capability of doing the same.In this sense the clinician can be looked upon as one

player and Nature in the form of the real disease as theother. In weighing the choice of a diagnosis (and wewill not beg the question of the mathematical basis ofthis, whether for example it is a bayesian concept), thephysician must be guided in his decision-making processnot only by the a-priori possibility of the disease existingbecause certain symptoms and signs are present, but alsoby his judgment of what will happen to the patient ifthat disease or some alternative exists. It may be arguedthat such judgment is also on a probability basis, but interms of the individual instance usually represents a yes/nodecision. Two almost trivial examples will suffice:A child of ten is admitted with acute abdominal pain, first

central and then in the right iliac fossa. There is fever andtenderness in the right lower abdomen. The differential

diagnosis lies (for simplicity) between acute appendicitisand acute non-specific mesenteric lymphadenitis. Often therewill be confirmatory signs of one or the other but not infre-quently the surgeon is left with the feeling that although heis doubtful about the existence of appendicitis he cannot besure. He will then operate prepared to have a live mistakerather than a dead certainty. What he is in fact intuitivelydoing is proceeding as if the patient had acute appendicitisbecause he knows that the pay-off of treating the patient inthis way and finding mesenteric adenitis is only the slightdisadvantage of a scar in the right iliac fossa, whereas theoutcome of treating acute appendicitis as mesenteric adenitismay be prolonged morbidity if not death. The pay-off thussuggests a particularly operational diagnosis although thelikelihood of the diagnosis a priori may, in fact, be much smallerthan that of an alternative which has a less favourable pay-off.The pay-offs in this " game " can be summarised as follows:

and even without such analysis it is obvious that the physician’ssafe strategy is to choose appendicitis whatever the patient has(i.e., if one regards Nature as the opponent, whatever Nature"

plays ").The second example is also conveniently taken from

pxdiatrics. A child has symptoms and signs suggestive ofacute osteomyelitis. If the diagnosis is not certain, few wouldrefrain from instituting chemotherapy

" as if " osteomyelitis

was present for, once again, the pay-off of delay is potentiallydisastrous, whereas the hazard of being wrong for the rightreasons is only slight. A further " as if " decision may haveto be made on the chemotherapeutic regimen adopted:although it can reasonably be assumed that the organisms willbe sensitive to one antibiotic it is customary to administerat least two with a broader combined spectrum in the recog-nition that the procedure rule must be " as if " organismsinsensitive to any single agent are present. Only when adiagnosis has been refined by bacteriological information, ifthis proves possible, is it then permissible to reduce thenumber of antibiotics in use.

3. Kahn, H. Thinking about the Unthinkable. New York, 1962.4. Von Neuman, L:, Morgenstern, O. On the Theory of Games and

Economic Behaviour. Princeton, 1947.

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Thus, particularly if we look upon diagnosisas a portal to a course of action, we mustrecognise that the physician’s method is basednot so much on the probability of an individualdisease being present but upon the outcome ifthat disease is present. Probability statementson occurrence (the bayesian approach), whilevaluable in relation to populations and series,are not necessarily guides to the actual be-haviour of any single individual in that series.Unless the probability of the occurrence of anydisease state is so small as to make it impossibleto contemplate (pregnancy in a male or car-cinoma of the prostate in the female are suitablyludicrous examples) then the consideration ofits existence in an individual must be taken intoaccount when the outcome and, therefore, themethod of procedure is being determined.Such operational or procedural diagnosis is thefrequent lot of the surgeon; it is only partiallyprobabilistic and deserves more attention thanit has so far received from the diagnostictheoretician.

Fig. I-Flow sheet, maze, or network for patient with central abdominal pain.

The two examples of pay-off decision-making givenabove are simple, but it does not take much thought toconceive more difficult or controversial decision-makingprocesses in relation both to diagnoses and therapy.Postoperative management, particularly in situationswhere a decision may lead to deployment of powerfulmethods of treatment (for example re-exploration of theabdomen, or the use of anticoagulants in a patient sus-pected of having deep-vein thrombosis) provide a richfield for complex weighing of outcomes: at the momentthe surgeon uses his background of " experience

" to

reach a decision but increasingly he must face the possi-bilities that he may need computational help.

HEURISTICS

William Hamilton the Scottish philosopher, coinedthe word " heuretic " to describe the logic of discoveryand invention. This term is rarely used, but " heuristic

"

(which can be defined as goal-seeking behaviour, the goalbeing already known or assumed) has now a respectableplace in the literature of sciences 5 and has recentlybecome part of the vocabulary of the diagnostic process.

Heuristic thinking plays a significant part in diagnosisin that frequently a diagnostic end-point or goal isdefined by circumstances; this may be illustrated byreference again to the emergency surgical managementof an acute abdominal complaint. The primary import-ant surgical decision is known before the diagnosticexercise is fully embarked upon: it is whether the abdo-men is to be opened or not. All inquiries will be directedto this end although, of course, they will be extended toinclude other measures so as to refine the diagnosistowards an xtiological label. But the pathway of inquiry,the clinical evaluation adopted, and the investigationsundertaken are goal seeking, or to use phraseology drawnfrom another discipline, are to a degree preprogrammedby the need to attain to a defined end-to operate or notto operate. It may be argued that this is both a limitedand a dangerous view to take of the diagnostic endeavour:limited, because it refers only to a practical situationrather than to a diagnostic philosophy; dangerous,because if the goal is too clearly defined a priori, it may5. Popper, K. R. The Logic of Scientific Discovery; appendix XI. New

York, 1959.

prove false and lead to neglect of the real problem. In

reply, it can only be said that practical situations of thiskind take up the majority of the clinician’s time and that,provided he is aware of his goal-seeking propensities, hecan modify the end-point, particularly if it becomesapparent from the outcome of initial heuristic activitiesthat the target is inappropriate. Thus, to take a crudeexample, if further investigation of the suspected acuteabdomen revealed both a history of angina and onlyminor abdominal findings, attention might clearly bedirected to a different goal-away from whether to

operate or not towards whether there is myocardialdisease.

In a sense all of the diagnostic process can be classedas heuristic for at any instant there is a defined aim-the elicitation of information, its correlation, and a con-clusion generated therefrom. We may liken the physicianmaking a diagnosis to a rat running a maze which hasalternative pathways of varying length leading to the

goal as well as the more usual terminal blind avenues.In some instances avenues which at first seem to lead tothe final or intermediate goals may be explored andrejected; in others what seems to be a subsidiary line ofinquiry leads once more into the main pathway. In eachinstance the rat or the physician is acting purposivelytowards what he thinks to be a goal. A fairly trivial

practical example will again suffice.A man aged sixty is admitted with vomiting and acute

central abdominal pain apparently of colicky nature; syste-matic inquiry reveals that he has also vague symptoms ofheadache, loss of concentration, and difficulty on micturition.The diagnostic process we have outlined requires us to makefurther inquiries into these symptoms to see if we can reach agoal of defining their importance or not in the context ofabdominal pain (fig. 1). In this case it may transpire thatthe first path leads nowhere and the second shows that diffi-culty on micturition followed his taking to bed with the pain;we retreat from both avenues to inquire further down themainstream of symptoms and signs related to mechanicalintestinal obstruction. But had it been found that there wasa long background suggestive of prostatic obstruction and

incipient renal failure we might have continued on to directquestions, or undertaken examinations and investigationswhich would have had as their ultimate goal the diagnosis ofursemic pseudo-obstruction.

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The attraction of this concept of goal-seeking behaviour is that it provides a

tenuous link with some aspects of learningtheory. We believe (although the evidenceis less than firm we might suppose) thatdiagnostic skill improves with practice.We know that an experienced rat runs amaze more efficiently in terms of timetaken and false avenues avoided. Thedifference between the tyro and the master

Fig. 2-Flow sheet for simple differential diagnosis of patient with upper-abdominalpain.

of the diagnostic process can be thought of in the sameterms-namely their ability to follow a goal-seeking patheffectively and with a minimum of false turns. This is thecombined result of familiarity with the route from previousattempts, an understanding of the nature of the goal, andcontinually reinforced motivation.

Consideration of diagnosis as a heuristic process leadsalso to the concept of a minimal path to a diagnosticgoal. Although we classically associate medical diagnosiswith a " gather the facts then analyse them " approach,when heuristic techniques are used we are much moreoften engaged in trying to -find the shortest length ofpathway to the diagnostic end-point. Length is definedhere as the smallest number of decisions on the ques-tions to ask, physical examinations to make, or specialinvestigations to be done. The situation is similar tothe end-game at chess where we can often find ways ofsolving the problem of mate in a small number of movesbut the most elegant situation is that where the numberof moves (decisions) is reduced to a minimum. Faced,then, with a number of different avenues of attack on aproblem, the experienced diagnostician is one who,either from his experience or from his ability to lookahead, can select the appropriate minimal pathway toreach a goal. In making such a selection he may mentallyexplore several avenues or even make short trips downthem only to withdraw on the face of evidence that tellshim they are unprofitable. Like the rat in the maze he

may explore side paths or even know of optimum routesunder special circumstances. Because we are repetitivein our attack on problems, there is some possibility thatthe goal-seeking minimum path used by the diagnosticiancan be identified and simulated by computer. In such acase the computer will be acting not as a probabilitycalculating machine but as a decision maker choosing orsuggesting alternative courses of action in the light ofexperience of a previous maze or, to use a term morecommon in computer language, network. The machinemay thus act as an aide memoire for the doctor, moni-toring his own decision-making and reminding him ofmatters as yet unexplored. In this sort of activity it canprofit by experience provided that the end result isrecorded and can be fed back into the system.Although we have looked upon the diagnostician and

his computer colleague as running a single channel orpath with a number of binary decision-points, there isno need to limit ourselves in this way. Double pathwaysmay be followed, the action being determined by theoutcome at two or more points simultaneously. Thiscan be simply illustrated by an example from emergencysurgery.A man presents with a history of alcoholism, acute upper

abdominal pain, tenderness, and minimal guarding in theepigastrium. Assuming, for simplicity, that the diagnosislies between acute pancreatitis and perforated peptic ulcer weundertake to follow a network illustrated in fig. 2. Theinvestigations to be performed in this instance are determina-

tion of serum-amylase (the pancreatitis avenue), an X-ray toshow gas under the diaphragm (peptic-ulcer avenue), and,possibly, laparotomy (both avenues). Instead of exploringsequentially, the surgeon arranges to traverse the first two

simultaneously and to structure his decision rules on theoutcome at the end of one, other or both. In retrospect he

may have not needed to do all that he has, but in prospectthis was the most satisfactory way of reaching a set of decisions.The apparently unsystematic and random actions of somephysicians in history taking, physical examination or investi-gation are related to their knowledge of minimal paths ofthis nature.

PATTERN RECOGNITION

The diagnostic process most difficult to understandis pattern recognition. The mechanisms behind our

power to distinguish the group of paintings of Van

Gogh from that by Gauguin or the poetry of Pope fromthat of Swift presumably rests upon the detection of apattern in both which has critical discriminatory features.Whether these features in turn rely upon individual

components of the picture or of the verse is not clear.

Certainly it is possible for an analysis to be based uponsuch a dissection of components (the textural pattern ofSt. Paul’s epistles is a good example) and of the rela-tionships between simple components, but whether thisconstitutes pattern recognition or is merely a long wayround to the same end result is not clear. Proponents ofgestalt psychology would hold that " form " is an entitydistinct from the sum of its components and that wemust search for the nature of form by other means thandissection; but how this is to be done in relation todisease is difficult to conceive. All that we can say atthe moment is that pattern recognition is a potentialmethod by which a diagnosis can be made and that ouruncontrolled observations of experienced clinicians leadus to believe that they may at times use this technique.

CONCLUSIONS

It can be argued that all that I have written here

merely formalises well-known and self-evident truths.This is so, but formal statements are a necessary pre-liminary to the use of computers and the attraction ofthese processes is that the first two (pay-off and heuristics)and the dissective aspects of pattern recognition can allbe handled by computer techniques. Although bayesianprocedures can be successfully applied to larger andlarger masses of observational data there is no a-prioriargument that diagnostic precision (without attemptingclearly to define this phrase) will undergo a consequentlinear increase except in narrow fields where there is

already available a taxonomy of analysed entities. Thisis not to under-estimate the ability of bayesian proceduresto discriminate populations on the basis of likelihood.Probabilistic techniques of this kind will find a con-

siderable use in separating populations for screeningpurposes into low risk and high risk groups for subse-quent more detailed analysis. Such diagnosis will be6. Simpson, G. G. Principles of Animal Taxonomy. New York, 1961.

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useful in the deployment of community resources.

However, computer routines that extend what we believeto be the physician’s own gaming and heuristic tech-niques may have greater ability to supplement the

general diagnostician. Finally, apart from high-speedanalysis of a complex into recognisable components orthe separation of a signal from a noisy background, it isdifficult to perceive a firm application of pattern recog-nition in relation to clinical diagnosis.

Probably the most important thing for the physicianas a teacher to realise is that with or without the inter-vention of the computer the techniques described applyin clinical practice. We have not yet fully taken thestudent into our confidence about our methods of diag-nosis making, probably because until the advent of thecomputer and the logical activity it demands we havenot endeavoured to understand our actions in the diag-nostic situation. It is scarcely surprising that the studentis confused when, with his background of training inthe formal deductive logic of the scientific laboratory,he sees the clinician adopt gaming, goal seeking, andpattern recognition. He is both confused and frustratedwhen in reply to his question-" why do you behave insuch a way ? "-the answer has been in the past,

" thisis the art of medicine." In searching for a new clinicalsystematics or an intelligible calculus of medicine theone to benefit should, one hopes, be the student. Further-more, if the techniques we use are analysable thereexists the opportunity of creating repetitive educationalsituations which should lead to the more rapid attain-ment of diagnostic skills.

7. Card, W. Med. An. 1967, 85, 9.

Medical Education

TEACHING AND RESEARCH IN

A DISTRICT GENERAL HOSPITAL

F. AVERY JONESC.B.E., M.D. Lond., F.R.C.P.

PHYSICIAN, CENTRAL MIDDLESEX HOSPITAL, LONDON N.W.10

THE evolution of the hospital service in the UnitedKingdom is clearly towards the building up of largegeneral district hospitals, and these, together with themain teaching-hospitals, will provide the specialisedmedical and surgical care for the country. Prof. D. A. K.Black has pointed out that " one of the big achievementsof the Health Service has been the wide dissemination of

good standards of hospital care." 1 Good standards inthe big district general hospitals can be achieved andmaintained only against a background of teaching andresearch. This paper aims to bring out the role of teachingand research in peripheral hospitals and will be illustratedby experience at the Central Middlesex Hospital.The district general hospitals provide an enormous

potential for clinical training, and the rising generationof doctors are particularly aware of this. Coming directfrom their teaching-hospitals they are at a phase of theircareer when they need and appreciate the continuedstimulus of teaching and research. Access to teaching,opportunities for research, forum for discussion, and goodsupporting diagnostic services are the essential ingredientsof an academic life. These stimulate confidence, profes-sional satisfaction, and an increased sense of responsibility,

1. Black, D. A. K. Lancet, 1968, i, 1308.

not only towards patients but also towards hospital andprofession; and lack of such facilities outside teaching-hospitals has encouraged many first-class men andwomen to emigrate. Those hospitals which have beenable to provide good facilities for teaching and researchhave had the best applicants for posts. This is reflectedin the rise in the standard of patient-care, and is par-ticularly noticeable and rewarding in relation to life-

threatening emergencies. The intensive hour-to-hourcare of patients by keen, well-trained registrars andhousemen pays good dividends in lowered mortality.

THE ESSENTIALS FOR ACADEMIC ACTIVITIES

If teaching and research are to be grafted on to thedaily life of a district general hospital, certain facilitiesare essential. These are:

(a) A lecture theatre for 80-150.(b) A small conference room to take 12-15 people.(c) A clinical room for teaching on each ward floor.(d) A clinical investigation unit of perhaps 8 all-purpose

rooms. These would include a consulting-room and a workshop.There should also be space for specialised investigations inroutine use (e.g., isotope studies, respiratory function tests) andspace for new techniques to be developed, especially thosewhich need clinical backing.

(e) A hospital medical library.(f) A department of medical photography and illustration.

Equally necessary are well-developed pathology andX-ray departments which must not only provide a highlevel of routine work, but also allow for extra studies tobe undertaken. Over some years these basic requirementshave now been largely achieved at Central Middlesex.Grafting teaching and research on to an older hospitalneeds structural adaptations. Fortunately hospitals whichwere constructed round the turn of the last century werewell built in ample grounds, and lend themselves to

necessary alterations. This has certainly been true at

Central Middlesex, built in 1904 on 60 acres as the ParkRoyal Infirmary. This has greatly facilitated the up-grading process which, like the improved staffing, hassteadily continued over the past 25 years.The hospital now plays a full role in undergraduate,

postgraduate, and specialist medical education.

TEACHING

Postgraduate TrainingThe appointment of a clinical tutor, a post at present

held by one of the surgeons, has made a major impact onthe organisation of teaching. This has been backed by theprovision of a good medical library. A weekly programme,displayed on a board in the centre of the hospital, recordsthe lectures, seminars, tutorials, weekly staff rounds, andin addition the special X-ray and histopathology demon-strations. These are all open not only to the staff workingat Central Middlesex Hospital but also to the staff in otherhospitals in the group. The development of a goodteaching programme depends on an adequate number ofbeds and medical staff. In the Central Middlesex Hospital153 medical staff look after 737 patients, and in thegroup there is a total of 257 doctors for 1285 beds. Theseare certainly sufficient for a teaching programme.

General practitioners are welcomed to any of the

teaching activities in the hospital, and local B.M.A.

meetings are held from time to time. Each year three

postgraduate refresher courses of one week each are heldin the hospital. The facilities for postgraduate teachingwill be greatly improved when an area medical centre hasbeen built. Plans have been prepared, and a public