CLINICAL
METHOD
IS ALL WRONG
H. A. F. DUDLEY. Surgical Unit, St. Mary’s Hospital, London, W2 1NY.
SUMMARY
Two models of diagnostic clinical behaviour are studied: the conventional in which data gathering precedes interpretation, and the sequential in which each item is evaluated as it is acquired and incorporated into decision making, usually of binary type. The second model is proposed as that more closely related to the reality of clinical practice and also as potentially more capable of exploiting intellectual resources and creating logistic economies.
educator) to reach a solution. The most likely method (because this is how he has predominantly been taught) will be a recall technique by which a particular whole pattern (say appendicitis or intestinal obstruction) has been stored in the memory and can be matched with the new set of data. However, this identification may be obscured by extraneous data or “noise” and furthermore recognition may be made difficult because the observed data set is incomplete. Further, the method is dependent upon adequate storage of selected patterns in the mind (brain) of the student. He is compelled to absorb many such patterns without question and independent of the frequency with which they will be encountered. This is a wasteful approach to teaching and learning, and largely negates the very considerable grounding that the learner has received in mechanisms. Finally, it is at a relatively low level of intellectual activity. The clinician in action does not adopt the student model. Instead he proceeds to make successive inferences. Pain? Yes. Its nature? Colic. Its associate? Vomiting. Inference: disordered smooth muscle contraction compatible with intestinal contraction against an obstruction. Jump therefore to other features which would characterize obstruction -absolute constipation? Yes. Sensation of distension? Yes. Audible borborygmi? Yes. Previous inferences are thus substantiated. This is now an indication to seek the physical signs in the abdomen of tympanitic distension and increased bowel sounds, and to order an abdominal film. A more structured interpretation of this inferential model with further questions directed towards aetiology is shown in Fig. 1. The important point is that models of this kind are sequential. They are of course selectively based on analysis of mechanism, on pattern recognition, or on both. However, they are capable of being more easily slanted towards the former. unlike the student model. What evidence do we have that the second model has some basis in reality? There is plenty of anecdotal experience going right back to the style of Joseph Bell who provided Conan Doyle with the background for Sherlock Holmes (5). No one would doubt the applicability of this
INTRODUCTION
This is not a well formulated hypothesis such as some which have appeared so far in Medical Hypotheses. Rather it is an attempt on a minor scale to undertake a Kuhnian gestalt switch (1) in relation to the way we think about clinical method. Like all good hypotheses it does not stand alone and elements of it have been enunciated in a medical context already by Medawar (2), myself (3), Taylor and his colleagues (4) and doubtless others whom I have not traced. In essence my thesis is this. The conventional educational model for the diagnostic process in medicine encourages the student to take a ‘history’ and to carry out a ‘clinical examination’. Both of these follow a highly structured pathway based upon the cumulative experience of some generations-a consensus of the generally relevant to medical enquiry as a whole. In particular, the examination is concentrated on the systematic elicitation of physical signs-that is potential indicators of abnormalities of structure or function against a reference frame of supposed normality. By contrast, the practical clinical model for diagnosis (and the qualification is an important one as I shall hope to show) is the sequential selection of items of data to form a chain of reasoning which leads from problem as presented by the patient to goal as seen by the doctor. The goal can be called a diagnosis, but the term requires further specification if it is to carry any precision.
MODELS
OF DIAGNOSIS
To elaborate the background slightly, let us take the example of a patient with an acute abdominal pain. The student would in his model explore the historical sequence of this, but would also conduct a systematic enquiry into many other items-past health, family history, to name but a few. He would then examine the whole patient. Only thereafter would he attempt to sift out data especially relevant to any possible causative mechanism for the pain. To do so he must shufRe through all the facts he has acquired. rearrange a proportion of them and then use some problem solving process (rarely if ever defined by the 164
Pain
Vomiting
Distension
intermittent
Constipation
Tympani
central
Borbarygmi
No
Historical
Physical
Small
intestinal
\ Small
Previous peritonitis
Fig.
I
1 /
bowel
obstruction
I
laparotomy
for
-
signs
obstruction
I
\
tes
tenderness
of simple
obstruction
colic
far too sweeping a generalisation, but it is borne out both by positive clinical behaviour and by the negative attitude often taken by the clinician towards disturbances in which it is not possible to demonstrate in life or after death a morbid change in the structure of the cell. It follows that the medical student-soon to become the clinician-is taught that, more often than not, his goal should be a diseasedisturbance diagnosis preferably in morbid anatomical terms. From time to time this will undoubtedly be correct; for example. I cannot carry out ablative treatment for a cancer of the breast until I have the morbid anatomical diagnosis. Equally, it can be wrong; for example, the decision whether or not to open the abdomen in a patient with acute abdominal pain is more important than the exact nature of the process within. From this necessarily brief discussion emerges the view that a more general definition of a diagnosis could be that it is the substance of a decision upon which action is based at any point in the patient’s course. In sequential terms it is a node from which separate pathways can be taken. In its simplest form there are two pathways and the decision is formulated in binary terms. Two matters follow. First, the necessity to formalise our description of the information at the node. Second, to acknowledge that the basis of decision at such a node is not purely binary even though the outcome is.
Adhesive
smal
I
bowel
obstruction
The “lumping” strategy used to combine data to form concepts in the diagnosis of intestinal obstruction.
model if he watches a busy outpatient session or alternatively a ‘work round’ on a hospital service. Less anecdotal studies of medical decision making are relatively few, but there is some evidence (6) to support the idea that sequential models are used, though generality of these (i.e.. that medical training or experience gives us a common view of sequential paths to problem solving) has been questioned (7). A recent clinical study has also established the power of sequential methods, given always that a goal can be defined (8). All the scanty evidence available points to heuristic, goal seeking behaviour in which some outcome+nitially known or hypothesised-is aimed for. In my example of acute abdominal pain the surgical objective or goal is a decision whether or not to open the abdomen. At this point and in the light of the statement just made, it is appropriate to our hypothesis to define diagnosis more precisely, because here again much of the thrust of conventional clinical method is too narrow if not completely wrong.
The structure of information at a node can best be defined by the use of the concept of a reference frame. By this I mean some convention that relates the items of data at this point to a particular class of items. When I say that: “acute abdominal pain which begins centrally, is associated with vomiting and is followed in a few hours by pain in the right iliac fossa and by the clinical signs of focal tenderness and muscle spasm, means appendicitis”; my reference frame is clinical. The pathologist who examines the appendix I have removed will confirm or confute the clinical diagnosis in a pathological frame on the basis of his morbid anatomical findings. Similarly, if I feel a hard, irregular lump in the breast of a middle aged woman my diagnosis of cancer is in a clinical frame. Alternatively the radiologist might look at the mammogram of the patient and see micro-calcification in a dense area and make a radiological diagnosis of cancer. Two outcomes can follow from the formulation of a diagnostic statement in a particular frame. Either, action as if the statement were wholly true, or the transfer of the diagnostic reasoning to another frame which may lead to a statement more appropriate to action. In the first example given the clinical diagnosis dictates action in the form of abdominal exploration: the frame of reference is actionappropriate. In the second, a frame transfer is necessary from clinical or radiological to morbid anatomical so as to avoid ablative surgery which could prove to be wrong. The clinical diagnosis is a decision statement, but only in relation to frame transfer, not definitive in the therapeutic sense. The definition of the term diagnosis we have now arrived at is a frame referenced action statement which leads to either of two outcomes-therapy or frame transfer. As we shall now see, there is a third possible happening, but to elucidate this we must briefly look at the basis
THE CONCEPT OF DIAGNOSIS All of us are prisoners of the facts and concepts available to us and the style of thinking that we inherit culturally. During the past hundred years or so the feature that has dominated all three in relation to medicine has been the cellular approach of morbid anatomical description followed by a gradually developing interest in morbid function which is usually correlated with abnormality of structure. These, in Kuhnian terms, have become the normal science of our generation and as such the conscious goals of our problem solving. (As far as I am aware no one has attempted to look at recent (i.e. post Enlightenment) medical scientific history in Kuhnian terms. Without necessarily totally accepting the idea of revolutionary as distinct from evolutionary change, the exercise might be a rewarding one. particularly now when social and economic events are pressing heavily on the conventional patterns of clinical science with a force that may compel a rapid evolution if not a revolution.) Thus, a diagnosis becomes synonymous
with either the demonstration
of some morbid
process or an inference as to its existence. Of course this is 165
of decision making at a node. Our discussion must be in outline only and will regard inductive inference in some form or another as justified or reasonable. (It is my experience that those outside the ranks of the philosophers and particularly medical men, have difficulty in understanding why it is even necessary to make this statement of convention. However, those who wish to gain an idea of the central nature of inductive inference to many logical problems may find some help in Passmore (9) and Swinburne (10). This being so, there will be evidence at a decision node which is based upon a frequentist analysis of past data. For example, if it is known that the combination of: middle age, a hard lump; irregularity of contour, occurs in 75% of patients who are subsequently found to have a breast cancer and hardly ever in those without, then we may loosely infer that the next time we see this combination the probability is .75 that the patient has breast cancer. Such an approach uses Bayesian statistics (or likelihood functions): we can summate the probability of association of each individual characteristic with the probability of the patient having breast cancer or the likelihood that our hypothesis of breast cancer is correct. (Bayesian summation is in a sense a number of small decision nodes applied to each item of data in a sequential model-see below). The ideal situation at a binary node is obviously when the evidence sums to give p [direction (a)] = 1 and p [direction (b)l = 0 or vice versa. However, this ideal is never realised even at an electronic binary decision node. In medicine, matters are usually much less certain and the problem is then the selection of an appropriate action level for probability of one or other path being correct if chosen. Action limits at binary decision nodes can be determined not only by the weight of the evidence (i.e., the posterior probability from previous experience), but also by psychological factors in the decision maker (4, 11) or by cost benefit considerations.
GENERAL
CLINICAL
PROBLEM
,
SOLVER
Do any
t -Choose small number of possibilities on basis of p_prjwL possibility(f0)
Is there a basis in mechanism for analysina observabid&& in any irank
is
I\
NO
t Incorporate into analysis
+ Perform highest remaining discriminatory test on list (llb)
*
--Ye.
Threshold
No??::
I Can pattern racwnition be
1 Is threshold reached for statement in this frame (S)(7) Ye/ 1
-I
‘No
St!ould on tp
;ie
therapeutic stctement
action be undertahan in this frame (S)
,,..Lt> Choose
Is frame
No/
now +appropriate for action (12) \Yes
/ -
t L Fig. 2
Formulate list using criteria
new test previous
(%
\\
/ Yes
b For this list now list tests in frame which will raise or lower probability of one or more on list. Rank tests in descending order of discrimination and ascending order of simpficity and safety (Ifa)
t Pr;key;;ties
(1)
t
1
t Choose frame which thought appropriate for action
observables
Take
\ therapeutic action
new
Select test thwapeutic
frame for (9) action
Confirms previous frame statement
A general problem solver for the sequential approach to diag-
now. For explanation see text. The B?ures in parentheses refer to detailed comments available on apphcation to the author.
results; new approaches to data handling; closer control of process (12). Here it is more appropriate to concentrate on whether the hypothesis is testable. I have already advanced some reasons for thinking that preliminary tests support rather than refute it. However, in this field we are not forced to make exclusive tests which lead to confident rejection of one hypothesis in favour of another (13). Rather we must ask if there are practical advantages to be gained from the choice of one strategy. The design of experiments for this purpose is difficult, but in so far as they have gone (14) support the logistic advantages of the approach. The intellectual appeal of this sequential model as I have developed it is threefold. First, it externalises the diagnostic process for examination and while leaning to some extent on the techniques made available by mathematicians from other fields, has an independence of its own. This externalisation permits study both by student and experimenter of the process in a way that has been denied to us by the accretive, pattern recognition approach. Second, and perhaps as a side issue (but an important one), the concepts of decision nets and reference frames liberates the word diagnosis and makes it in my mind more flexible and useful. Third, it forces the clinician to choose (on the basis of Fig. 2) between arguments based on mechanism and on pattern recognition. Either may be appropriate: indeed it is part of the history of the understanding of medical problems that we proceed from an identification of patterns at a clinical level to the elucidation of mechanisms at whatever depth or height of organisation is appropriate to our
A GENERAL MEDICAL PROBLEM SOLVER We are now in a position to construct an overall hypothesis which attempts to explain clinical diagnostic behaviour and incorporates the terms and definitions that I have outlined. This is shown in Fig. 2. It is not inappropriate to call it a general medical problem solver. It is important to remind ourselves that this alternative method of exploiting clinical method deals with diagnosis alone. The systematic elucidation of facts may be necessary to establish a data base so as to guide management and make it safe, or for epidemiological studies. However, even in the management role we are bound to be selective in what we elicit and it is not conceptually difficult to construct a flow chart for that purpose which resembles that in Fig. 2, but is designed for data accretion in relation to the management of specific situations. My purpose here is not to elaborate further on the possible practical advantages of this alternative hypothesis of clinical method, though some of these are clear: the elimination of paradoxical behaviour by teachers to which I have already referred; more economical methods of getting 166
needs. Therefore we may at any point in time of scientific knowledge only have the information to make a pattern recognition statement in a clinical frame of reference. Alternatively. we may both be able to and need to dissect mechanism to varying depths. Examples abound, but if I could stick to my surgical last we could contrast the clinical quasi-pattern recognition approach to the diagnosis of acute appendicitis with the microbiological knowledge required to make decisions about preventive chemotherapy in this disorder and the biochemical understanding necessary to handle the patient who develops ileus or a fistula. In internal medicine we can compare the frame required to make a diagnosis of liver impairment on clinical grounds with that required to ascertain the cause-an exercise that may sometimes be biochemical, sometimes genetic, sometimes immunological.
new approach is indicated which is more open ended and offers us the chance of escape from a number of impasses both scientific and social. A
5. 6. I. 8. 9. 10.
CONCLUSION Clinical method is not all wrong and clearly I have chosen an attention-seeking title for my hypothesis. Nevertheless, no one who both practises and teaches medicine today can be blind to the fact that the conventional mode1 is clumsy, non-adaptive and tends to add on new techniques rather than incorporate them into a logical, heuristic pattern.
11. 12. 13. 14.
167
REFERENCES Kuhn T. Structure of ScientiJic Revolutions. Chicago University Press. 1970. Medawar P. Induction and Intuition in ScientiJc Thought. Methuen, London, 1969 Dudley H. Tasks for clinicians: the diagnostic process. Med J Austr. I, 37, 1969 Taylor TR, Aitchison J, McGirr EM. Doctors as decision makers: A computer assisted study of cognitive skills. Brit Med J. 3, 35, 1971 Pearson H. Conan Doyle: his Life and Art. Methuen, London, 1943 Oldham J. Preliminary investigations into surgeons diagnosing abdominal pain. J Roy Coil Surg Edin. 18, 79, 1973 Leaper DJ, Gill PW, Staniland JR, Horrocks JC, de Dombal FT. Clinical diagnostic process: An analysis. Brit Med J. 3, 569, 1973 Essex BJ Approach to rapid problem solving in medicine. Brit Med J. 3, 34, 1975 Passmore J. A Hundred Years of Philosophy. Penguin Books, London, 1968 Swinburne R. The Justification of Induction. Oxford University Press, 1974 de Dombal FT, Horrocks JC, Staniland JR, Guillou PJ. Production of artificial case histories by using a small computer. Brit Med J. 2, 578, 1971 Dudley H. Necessity for surgical audit. Brit Med J. 1, 275, 1974 Popper K. Logic of Scientific Discovery. Hutchinson, London, 1959 Dudley H. Clinical Algorithms. In Advanced Medical Systems: Issues and Challenges, p. 191, ed. C. D. Flagle, Stratton, New York, 1975
METHOD
IS ALL WRONG
H. A. F. DUDLEY. Surgical Unit, St. Mary’s Hospital, London, W2 1NY.
SUMMARY
Two models of diagnostic clinical behaviour are studied: the conventional in which data gathering precedes interpretation, and the sequential in which each item is evaluated as it is acquired and incorporated into decision making, usually of binary type. The second model is proposed as that more closely related to the reality of clinical practice and also as potentially more capable of exploiting intellectual resources and creating logistic economies.
educator) to reach a solution. The most likely method (because this is how he has predominantly been taught) will be a recall technique by which a particular whole pattern (say appendicitis or intestinal obstruction) has been stored in the memory and can be matched with the new set of data. However, this identification may be obscured by extraneous data or “noise” and furthermore recognition may be made difficult because the observed data set is incomplete. Further, the method is dependent upon adequate storage of selected patterns in the mind (brain) of the student. He is compelled to absorb many such patterns without question and independent of the frequency with which they will be encountered. This is a wasteful approach to teaching and learning, and largely negates the very considerable grounding that the learner has received in mechanisms. Finally, it is at a relatively low level of intellectual activity. The clinician in action does not adopt the student model. Instead he proceeds to make successive inferences. Pain? Yes. Its nature? Colic. Its associate? Vomiting. Inference: disordered smooth muscle contraction compatible with intestinal contraction against an obstruction. Jump therefore to other features which would characterize obstruction -absolute constipation? Yes. Sensation of distension? Yes. Audible borborygmi? Yes. Previous inferences are thus substantiated. This is now an indication to seek the physical signs in the abdomen of tympanitic distension and increased bowel sounds, and to order an abdominal film. A more structured interpretation of this inferential model with further questions directed towards aetiology is shown in Fig. 1. The important point is that models of this kind are sequential. They are of course selectively based on analysis of mechanism, on pattern recognition, or on both. However, they are capable of being more easily slanted towards the former. unlike the student model. What evidence do we have that the second model has some basis in reality? There is plenty of anecdotal experience going right back to the style of Joseph Bell who provided Conan Doyle with the background for Sherlock Holmes (5). No one would doubt the applicability of this
INTRODUCTION
This is not a well formulated hypothesis such as some which have appeared so far in Medical Hypotheses. Rather it is an attempt on a minor scale to undertake a Kuhnian gestalt switch (1) in relation to the way we think about clinical method. Like all good hypotheses it does not stand alone and elements of it have been enunciated in a medical context already by Medawar (2), myself (3), Taylor and his colleagues (4) and doubtless others whom I have not traced. In essence my thesis is this. The conventional educational model for the diagnostic process in medicine encourages the student to take a ‘history’ and to carry out a ‘clinical examination’. Both of these follow a highly structured pathway based upon the cumulative experience of some generations-a consensus of the generally relevant to medical enquiry as a whole. In particular, the examination is concentrated on the systematic elicitation of physical signs-that is potential indicators of abnormalities of structure or function against a reference frame of supposed normality. By contrast, the practical clinical model for diagnosis (and the qualification is an important one as I shall hope to show) is the sequential selection of items of data to form a chain of reasoning which leads from problem as presented by the patient to goal as seen by the doctor. The goal can be called a diagnosis, but the term requires further specification if it is to carry any precision.
MODELS
OF DIAGNOSIS
To elaborate the background slightly, let us take the example of a patient with an acute abdominal pain. The student would in his model explore the historical sequence of this, but would also conduct a systematic enquiry into many other items-past health, family history, to name but a few. He would then examine the whole patient. Only thereafter would he attempt to sift out data especially relevant to any possible causative mechanism for the pain. To do so he must shufRe through all the facts he has acquired. rearrange a proportion of them and then use some problem solving process (rarely if ever defined by the 164
Pain
Vomiting
Distension
intermittent
Constipation
Tympani
central
Borbarygmi
No
Historical
Physical
Small
intestinal
\ Small
Previous peritonitis
Fig.
I
1 /
bowel
obstruction
I
laparotomy
for
-
signs
obstruction
I
\
tes
tenderness
of simple
obstruction
colic
far too sweeping a generalisation, but it is borne out both by positive clinical behaviour and by the negative attitude often taken by the clinician towards disturbances in which it is not possible to demonstrate in life or after death a morbid change in the structure of the cell. It follows that the medical student-soon to become the clinician-is taught that, more often than not, his goal should be a diseasedisturbance diagnosis preferably in morbid anatomical terms. From time to time this will undoubtedly be correct; for example. I cannot carry out ablative treatment for a cancer of the breast until I have the morbid anatomical diagnosis. Equally, it can be wrong; for example, the decision whether or not to open the abdomen in a patient with acute abdominal pain is more important than the exact nature of the process within. From this necessarily brief discussion emerges the view that a more general definition of a diagnosis could be that it is the substance of a decision upon which action is based at any point in the patient’s course. In sequential terms it is a node from which separate pathways can be taken. In its simplest form there are two pathways and the decision is formulated in binary terms. Two matters follow. First, the necessity to formalise our description of the information at the node. Second, to acknowledge that the basis of decision at such a node is not purely binary even though the outcome is.
Adhesive
smal
I
bowel
obstruction
The “lumping” strategy used to combine data to form concepts in the diagnosis of intestinal obstruction.
model if he watches a busy outpatient session or alternatively a ‘work round’ on a hospital service. Less anecdotal studies of medical decision making are relatively few, but there is some evidence (6) to support the idea that sequential models are used, though generality of these (i.e.. that medical training or experience gives us a common view of sequential paths to problem solving) has been questioned (7). A recent clinical study has also established the power of sequential methods, given always that a goal can be defined (8). All the scanty evidence available points to heuristic, goal seeking behaviour in which some outcome+nitially known or hypothesised-is aimed for. In my example of acute abdominal pain the surgical objective or goal is a decision whether or not to open the abdomen. At this point and in the light of the statement just made, it is appropriate to our hypothesis to define diagnosis more precisely, because here again much of the thrust of conventional clinical method is too narrow if not completely wrong.
The structure of information at a node can best be defined by the use of the concept of a reference frame. By this I mean some convention that relates the items of data at this point to a particular class of items. When I say that: “acute abdominal pain which begins centrally, is associated with vomiting and is followed in a few hours by pain in the right iliac fossa and by the clinical signs of focal tenderness and muscle spasm, means appendicitis”; my reference frame is clinical. The pathologist who examines the appendix I have removed will confirm or confute the clinical diagnosis in a pathological frame on the basis of his morbid anatomical findings. Similarly, if I feel a hard, irregular lump in the breast of a middle aged woman my diagnosis of cancer is in a clinical frame. Alternatively the radiologist might look at the mammogram of the patient and see micro-calcification in a dense area and make a radiological diagnosis of cancer. Two outcomes can follow from the formulation of a diagnostic statement in a particular frame. Either, action as if the statement were wholly true, or the transfer of the diagnostic reasoning to another frame which may lead to a statement more appropriate to action. In the first example given the clinical diagnosis dictates action in the form of abdominal exploration: the frame of reference is actionappropriate. In the second, a frame transfer is necessary from clinical or radiological to morbid anatomical so as to avoid ablative surgery which could prove to be wrong. The clinical diagnosis is a decision statement, but only in relation to frame transfer, not definitive in the therapeutic sense. The definition of the term diagnosis we have now arrived at is a frame referenced action statement which leads to either of two outcomes-therapy or frame transfer. As we shall now see, there is a third possible happening, but to elucidate this we must briefly look at the basis
THE CONCEPT OF DIAGNOSIS All of us are prisoners of the facts and concepts available to us and the style of thinking that we inherit culturally. During the past hundred years or so the feature that has dominated all three in relation to medicine has been the cellular approach of morbid anatomical description followed by a gradually developing interest in morbid function which is usually correlated with abnormality of structure. These, in Kuhnian terms, have become the normal science of our generation and as such the conscious goals of our problem solving. (As far as I am aware no one has attempted to look at recent (i.e. post Enlightenment) medical scientific history in Kuhnian terms. Without necessarily totally accepting the idea of revolutionary as distinct from evolutionary change, the exercise might be a rewarding one. particularly now when social and economic events are pressing heavily on the conventional patterns of clinical science with a force that may compel a rapid evolution if not a revolution.) Thus, a diagnosis becomes synonymous
with either the demonstration
of some morbid
process or an inference as to its existence. Of course this is 165
of decision making at a node. Our discussion must be in outline only and will regard inductive inference in some form or another as justified or reasonable. (It is my experience that those outside the ranks of the philosophers and particularly medical men, have difficulty in understanding why it is even necessary to make this statement of convention. However, those who wish to gain an idea of the central nature of inductive inference to many logical problems may find some help in Passmore (9) and Swinburne (10). This being so, there will be evidence at a decision node which is based upon a frequentist analysis of past data. For example, if it is known that the combination of: middle age, a hard lump; irregularity of contour, occurs in 75% of patients who are subsequently found to have a breast cancer and hardly ever in those without, then we may loosely infer that the next time we see this combination the probability is .75 that the patient has breast cancer. Such an approach uses Bayesian statistics (or likelihood functions): we can summate the probability of association of each individual characteristic with the probability of the patient having breast cancer or the likelihood that our hypothesis of breast cancer is correct. (Bayesian summation is in a sense a number of small decision nodes applied to each item of data in a sequential model-see below). The ideal situation at a binary node is obviously when the evidence sums to give p [direction (a)] = 1 and p [direction (b)l = 0 or vice versa. However, this ideal is never realised even at an electronic binary decision node. In medicine, matters are usually much less certain and the problem is then the selection of an appropriate action level for probability of one or other path being correct if chosen. Action limits at binary decision nodes can be determined not only by the weight of the evidence (i.e., the posterior probability from previous experience), but also by psychological factors in the decision maker (4, 11) or by cost benefit considerations.
GENERAL
CLINICAL
PROBLEM
,
SOLVER
Do any
t -Choose small number of possibilities on basis of p_prjwL possibility(f0)
Is there a basis in mechanism for analysina observabid&& in any irank
is
I\
NO
t Incorporate into analysis
+ Perform highest remaining discriminatory test on list (llb)
*
--Ye.
Threshold
No??::
I Can pattern racwnition be
1 Is threshold reached for statement in this frame (S)(7) Ye/ 1
-I
‘No
St!ould on tp
;ie
therapeutic stctement
action be undertahan in this frame (S)
,,..Lt> Choose
Is frame
No/
now +appropriate for action (12) \Yes
/ -
t L Fig. 2
Formulate list using criteria
new test previous
(%
\\
/ Yes
b For this list now list tests in frame which will raise or lower probability of one or more on list. Rank tests in descending order of discrimination and ascending order of simpficity and safety (Ifa)
t Pr;key;;ties
(1)
t
1
t Choose frame which thought appropriate for action
observables
Take
\ therapeutic action
new
Select test thwapeutic
frame for (9) action
Confirms previous frame statement
A general problem solver for the sequential approach to diag-
now. For explanation see text. The B?ures in parentheses refer to detailed comments available on apphcation to the author.
results; new approaches to data handling; closer control of process (12). Here it is more appropriate to concentrate on whether the hypothesis is testable. I have already advanced some reasons for thinking that preliminary tests support rather than refute it. However, in this field we are not forced to make exclusive tests which lead to confident rejection of one hypothesis in favour of another (13). Rather we must ask if there are practical advantages to be gained from the choice of one strategy. The design of experiments for this purpose is difficult, but in so far as they have gone (14) support the logistic advantages of the approach. The intellectual appeal of this sequential model as I have developed it is threefold. First, it externalises the diagnostic process for examination and while leaning to some extent on the techniques made available by mathematicians from other fields, has an independence of its own. This externalisation permits study both by student and experimenter of the process in a way that has been denied to us by the accretive, pattern recognition approach. Second, and perhaps as a side issue (but an important one), the concepts of decision nets and reference frames liberates the word diagnosis and makes it in my mind more flexible and useful. Third, it forces the clinician to choose (on the basis of Fig. 2) between arguments based on mechanism and on pattern recognition. Either may be appropriate: indeed it is part of the history of the understanding of medical problems that we proceed from an identification of patterns at a clinical level to the elucidation of mechanisms at whatever depth or height of organisation is appropriate to our
A GENERAL MEDICAL PROBLEM SOLVER We are now in a position to construct an overall hypothesis which attempts to explain clinical diagnostic behaviour and incorporates the terms and definitions that I have outlined. This is shown in Fig. 2. It is not inappropriate to call it a general medical problem solver. It is important to remind ourselves that this alternative method of exploiting clinical method deals with diagnosis alone. The systematic elucidation of facts may be necessary to establish a data base so as to guide management and make it safe, or for epidemiological studies. However, even in the management role we are bound to be selective in what we elicit and it is not conceptually difficult to construct a flow chart for that purpose which resembles that in Fig. 2, but is designed for data accretion in relation to the management of specific situations. My purpose here is not to elaborate further on the possible practical advantages of this alternative hypothesis of clinical method, though some of these are clear: the elimination of paradoxical behaviour by teachers to which I have already referred; more economical methods of getting 166
needs. Therefore we may at any point in time of scientific knowledge only have the information to make a pattern recognition statement in a clinical frame of reference. Alternatively. we may both be able to and need to dissect mechanism to varying depths. Examples abound, but if I could stick to my surgical last we could contrast the clinical quasi-pattern recognition approach to the diagnosis of acute appendicitis with the microbiological knowledge required to make decisions about preventive chemotherapy in this disorder and the biochemical understanding necessary to handle the patient who develops ileus or a fistula. In internal medicine we can compare the frame required to make a diagnosis of liver impairment on clinical grounds with that required to ascertain the cause-an exercise that may sometimes be biochemical, sometimes genetic, sometimes immunological.
new approach is indicated which is more open ended and offers us the chance of escape from a number of impasses both scientific and social. A
5. 6. I. 8. 9. 10.
CONCLUSION Clinical method is not all wrong and clearly I have chosen an attention-seeking title for my hypothesis. Nevertheless, no one who both practises and teaches medicine today can be blind to the fact that the conventional mode1 is clumsy, non-adaptive and tends to add on new techniques rather than incorporate them into a logical, heuristic pattern.
11. 12. 13. 14.
167
REFERENCES Kuhn T. Structure of ScientiJic Revolutions. Chicago University Press. 1970. Medawar P. Induction and Intuition in ScientiJc Thought. Methuen, London, 1969 Dudley H. Tasks for clinicians: the diagnostic process. Med J Austr. I, 37, 1969 Taylor TR, Aitchison J, McGirr EM. Doctors as decision makers: A computer assisted study of cognitive skills. Brit Med J. 3, 35, 1971 Pearson H. Conan Doyle: his Life and Art. Methuen, London, 1943 Oldham J. Preliminary investigations into surgeons diagnosing abdominal pain. J Roy Coil Surg Edin. 18, 79, 1973 Leaper DJ, Gill PW, Staniland JR, Horrocks JC, de Dombal FT. Clinical diagnostic process: An analysis. Brit Med J. 3, 569, 1973 Essex BJ Approach to rapid problem solving in medicine. Brit Med J. 3, 34, 1975 Passmore J. A Hundred Years of Philosophy. Penguin Books, London, 1968 Swinburne R. The Justification of Induction. Oxford University Press, 1974 de Dombal FT, Horrocks JC, Staniland JR, Guillou PJ. Production of artificial case histories by using a small computer. Brit Med J. 2, 578, 1971 Dudley H. Necessity for surgical audit. Brit Med J. 1, 275, 1974 Popper K. Logic of Scientific Discovery. Hutchinson, London, 1959 Dudley H. Clinical Algorithms. In Advanced Medical Systems: Issues and Challenges, p. 191, ed. C. D. Flagle, Stratton, New York, 1975
