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Inductive foraging: improving the diagnostic yield of primary care consultations.

27 Feb 2014-European Journal of General Practice (Eur J Gen Pract)-Vol. 20, Iss: 1, pp 69-73

TL;DR: It is suggested that ‘inductive foraging’ is a relevant and appropriate mode of data acquisition for the first part of the patient encounter, and inductive foraging is a rational and efficient diagnostic strategy.
Abstract: Background: Physicians attempting to make a diagnosis arrive at specific hypotheses early in their encounter with patients. Further data are collected in the light of these early hypotheses. While this hypothetico-deductive model has been accepted as both a description of physicians’ data gathering and a norm, little attention has been paid to the preceding stage of the consultation.Hypothesis: It is suggested that ‘inductive foraging’ is a relevant and appropriate mode of data acquisition for the first part of the patient encounter.Methods: Research evidence from cognitive psychology and medical reasoning research is discussed.Results: With inductive foraging, ‘pattern failure’ rather than ‘pattern recognition’ is the mode of discovery. Largely, guidance should be left to the patient to lead the clinician into areas where departures from normality are to be found. This is in contrast to active and focused ‘deductive inquiry,’ which should be used only after most aetiologies, but a few have elimin...

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Background Paper
Inductive foraging: Improving the diagnostic yield of
primary care consultations
Norbert Donner-Banzhoff MD, MHSc
& Ralph Hertwig PhD
Department of General Practice, University of Marburg, Germany, and
Department of Adaptive Rationality, Max-Planck-Institute for
Human Development, Berlin, Germany
Medical practitioners reasoning and data collection is
often framed as hypothetico-deductive (1). According to
this view, clinicians form a hypothesis based on their fi rst
impression early in the consultation with the patient.
More hypotheses, i.e. possible diagnoses, are added, but
their number is usually limited. Further data collection
by history taking and physical examination is guided
by these early hypotheses. Once the likelihood of a
diagnosis has reached a suffi ciently high threshold, data
collection is stopped, and either treatment is started or
further testing is performed.
Premature closure is said to occur when clinicians
stop their data collection too early and, as a conse-
quence, miss important information. This has been iden-
tifi ed as an important source of diagnostic error (2 4).
In this view, premature closure can happen only after the
rst hypothesis has arisen in the clinician s mind. To date,
little attention has been paid to the period before a
hypothesis has been formed. We would suggest that at
European Journal of General Practice, 2014; 20: 69–73
ISSN 1381-4788 print/ISSN 1751-1402 online © 2014 Informa Healthcare
DOI: 10.3109/13814788.2013.805197
· Hypothetico-deductive reasoning has become the orthodox descriptive and normative model. However, this is
not the whole story.
· ‘ Inductive Foraging ’ is a highly effi cient data gathering strategy for generalist practice, when a large number of
aetiologies have to be considered.
· Research from clinical reasoning research, cognitive psychology and education, support the concept of
‘ inductive foraging ’.
Background: Physicians attempting to make a diagnosis arrive at specifi c hypotheses early in their encounter with patients. Further
data are collected in the light of these early hypotheses. While this hypothetico-deductive model has been accepted as both a
description of physicians data gathering and a norm, little attention has been paid to the preceding stage of the consultation.
Hypothesis : It is suggested that inductive foraging is a relevant and appropriate mode of data acquisition for the fi rst part of the
patient encounter.
Methods : Research evidence from cognitive psychology and medical reasoning research is discussed.
Results: With inductive foraging, pattern failure rather than pattern recognition is the mode of discovery. Largely, guidance should
be left to the patient to lead the clinician into areas where departures from normality are to be found. This is in contrast to active
and focused deductive inquiry, which should be used only after most aetiologies, but a few have eliminated.
Implication : Especially when the prevalence of serious disease is low, and a wide range of diagnoses must be evaluated, such as in
General Practice, inductive foraging is a rational and effi cient diagnostic strategy. Previously, too little attention has been paid to
the initial stage of the consultation. Premature closure at this point may result in diagnostic error.
decision making , uncertainty , cognition , perception , judgement , diagnosis , general practice , family practice
Conference Presentations : NDB presented parts of this article at the COGITA working group of the European General Practice Research Network, Z ü rich, Switzerland,
October 2010.
Correspondence: Norbert Donner-Banzhoff , Department of General Practice, University of Marburg, Karl-von-Frisch-Str. 4, D-35043 Marburg, Germany. E-mail
(Received 12 October 2012; accepted 19 April 2013)
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70 N. Donner-Banzhoff & R. Hertwig
this, the hypothesis-generation phase is of crucial impor-
tance for the diagnostic outcome of the consultation
especially in General Practice.
We are suggesting here that a stage to be called induc-
tive foraging precedes hypothesis formation. Ideally,
the space of possible symptoms is searched with an
open mind on the side of the physician. To what degree
clinicians are able to restrain themselves at this stage,
determines the number and appropriateness of diag-
nostic hypotheses considered for an individual patient.
Thus, the foraging stage is an important part of the diag-
nostic process and deserves more attention from clini-
cians, researchers, and educators. We contend that
suffi cient evidence is available to make some tentative
recommendations regarding tactics to be used during
inductive foraging.
During the inductive foraging stage of the consulta-
tion, the patient leads the clinician to areas that are
unusual or worrisome. Here, the predominant diagnostic
strategy may be one of pattern failure rather than pat-
tern recognition (5). Lewis likens the situation to an LCD
monitor screen the working of which one is hardly aware
of. However, if a pixel is not working, one s eye is inevi-
tably drawn to it with the resulting feeling that some-
thing is wrong. Accordingly, in the consultation there is
often a stage when single pieces of information cannot
yet be matched to a pattern. This will stimulate further
probing of unusual phenomena until the range of pos-
sibilities is narrowed into a specifi c hypothesis. Another
possibility is the impression, that something does not
feel right, or that a particular patient is not herself (see
below for meningococcal infection as an example). As
long as no departure from normal is noticed, the default
is the assumption that there is no pathology deserving
further investigation, at least as long the problem space
has been foraged to a suffi cient extent. Inductive forag-
ing has universal application even beyond medical diag-
nosis (6), but it is especially suitable for primary care
where the prevalence of serious disease is low but a
wide range of possibilities must be explored.
Although, our suggestion of inductive foraging is novel
as a diagnostic strategy, there is indirect evidence in the
literature supporting the concept. From his analysis of
Dutch general practitioners (GPs) working with simu-
lated patients, Ridderikhof (7) concluded that inductive
reasoning is the predominant mode of data collection
and reasoning. In his view, information from the patients
serves the process of evoking hypotheses rather than
testing them. Ridderikhof highlighted the speculative
and erratic nature of the hypothesis-generating process,
which he considered at odds with professional account-
ability and the scientifi c foundation of medical practice.
Bordage et al. (8) saw what they call a responsive
mode of enquiry in a more positive light. They encour-
aged clinicians to alternate their thinking between a
deterministic mode, in which questions related to a
specifi c hypothesis are being asked, and a responsive
mode, paying attention to information off ered by the
The main conclusion drawn from the Medical Inquiry
Project (1) is that a purely inductive method of data gath-
ering is never used by physicians, but that hypotheses
are formed early and guide further work-up. However,
even in this study with standardized patients diagnostic
accuracy was associated with the amount of cues
acquired. In some cases, withholding hypothesis genera-
tion until suffi cient data had been obtained apparently
resulted in better diagnosis. A strategy of inductive
reasoning was associated with diagnostic success in a
think-aloud study of paper cases for medical students
and experienced gastroenterologists (9).
Granier et al. report the retrospective accounts of
Welsh GPs managing children with meningococcal
disease (10). This is an interesting case study since the
condition is so rare that GPs cannot gather suffi cient
experience diagnosing it. Instead, they were using depar-
tures from an assumed normal state as an indication of
a serious problem. The behaviour of parents provided
cues in some cases, such as a mother of three children,
usually coping well, suddenly bursting into tears. Another
point of reference was the image of benign infection.
Children being lethargic, not interacting with either their
parents or the GPs, or crying in an unusual way pre-
sented exceptions to an assumed normality of benign,
self-limiting infection. The matching of information to a
positive pattern was not yet possible at that stage, so
physicians reasoning rather took the form of pattern
failure. This still resulted in optimal decisions, i.e. imme-
diate transfer to hospital. A study of Danish family physi-
cians diagnosing neglect and abuse in children showed
similar results (11). These fi ndings have led to the pos-
tulate that a family of discrepancy heuristics underlies a
large part of diagnostic assessment in primary care prac-
tice (12). Their frame of reference may be previous expe-
rience with a particular patient (within-person
comparison), or typical behaviour of similar patients
(between-person comparison). In some European coun-
tries, GPs are encouraged to act on their gut feelings or
their sense of alarm (13 14).
Using the background of Popper s theory of falsifi cation
(15) as one benchmark within the context of discovery,
numerous investigators have deplored the seemingly
irrational behaviour of subjects confronted with rule
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Inductive foraging 71
discovery or diagnostic tasks. Instead of aiming to refute
their hypotheses by searching for disconfi rming evi-
dence, most people seek information that confi rms the
idea (hypothesis) they have formed. Accordingly, clini-
cians seek abnormal symptoms or fi ndings that fi t their
hypotheses. For rational inference, however, one should
evaluate a single piece of information, such as fever,
across hypotheses, and thus draw conclusions from the
absence as well as from the presence of a signal.
Klayman and Ha, however, have suggested that a
confi rmative or positive test strategy can be appropriate,
especially when concrete, task-specifi c information is
lacking, or cognitive demands are high (16). According
to this strategy, individuals search for and examine
instances in which the target behaviour, property, or
event is expected to occur, as opposed to searching for
instances where it is not expected to occur under the
hypothesis entertained. They reason that under certain
circumstances positive evidence is more likely to prove
a hypothesis wrong. This is the case in probabilistic set-
tings and where the target event is rare. The General
Practice consultation is a good example. Here, the prev-
alence of serious disease is low and related pathological
ndings are rare. For each patient, the most likely
hypothesis is thus absence of serious disease. Accord-
ingly, it is the presence of an abnormality that discon-
rms the most likely hypothesis. The presence of an
abnormality is more informative than confi rmation of its
absence. However, the reverse is true if the probability
of the target category, i.e. disease, is high. In that case,
the hypothesis is effi ciently tested also by negative evi-
dence, i.e. absence of fi ndings (16,17).
Human beings fi nd it diffi cult to evaluate isolated
information, especially if presented in a quantitative way.
Often only the provision of an anchor for comparison
enables individuals to evaluate a statement. There is
extensive research showing how anchoring, i.e. compar-
ing a stimulus with a frame of reference, can mislead a
decision-maker if taken to a diff erent context (18 20).
However, despite this line of research, one should not
forget that comparing a particular fi nding with a frame of
reference provides a powerful and ubiquitous heuristic in
human and clinical decision-making. What constitutes
information in the clinical encounter can only be defi ned
by comparison with a reference. Pain experienced by a
patient with chronic rheumatoid arthritis on one of her
good days can be devastating for a person who has not
had musculoskeletal problems before. At this stage,
therefore, it makes sense to leave the initiative to the
patient to lead the physician to problem areas, i.e. areas
where well-being or function diff ers from normal, which
can thus provide clinically relevant information. In this
way, the clinician can make productive use of the frame
of reference defi ned by the patient.
Interestingly, the developers of a computer-based
general medical expert system concluded that one of the
limitations of their product is the inability to take a broad
perspective of a case presented. The system would suff er
from a tunnel vision, and only after having arrived at
specifi c diagnosis would the links to their sophisticated
data base provide satisfactory diagnostic results (21,22).
This example from applied artifi cial intelligence under-
lines the importance of the foraging stage, but also the
diffi culty delegating the task to a machine.
By premature closure, authors usually mean the end of
a phase of specifi c hypotheses evaluation. We suggest
the term deductive inquiry for this phase since reason-
ing goes from propositions (hypothesis) to data gathered
by history taking or examination of the patient. We con-
tend that premature closure can also occur earlier than
that, marking the end of the preceding inductive forag-
ing phase and starting deductive inquiry prematurely
(see Figure 1). This may result in missing relevant diag-
nostic information. Instead, patients should be encour-
aged to elaborate on symptoms or, more generally, on
deviations from their normal state and associated con-
cerns. This strategy promises to yield a rich set of infor-
mation and does not foreclose the retrieval of information
not expected by the clinician. It amounts to a positive
test strategy in so far as the patient can be expected to
focus on noteworthy occurrences of unusual events,
such as symptoms and concerns. In contrast, adopting a
question-and-answer-mode early on risks that the
patient volunteers only the information that has been
explicitly asked for.
There seem to be compelling reasons for physicians
to interrupt their patients early in the consultation
(23,24). To expedite the consultation and thereby save
time is an obvious motive for busy clinicians. A more
subtle consideration refers to re-interpretation of
information in view of a diagnostic hypothesis. Once
Inductive foraging Deductive
Figure 1. Stages of the clinical encounter and related modes of
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72 N. Donner-Banzhoff & R. Hertwig
frequent, and often no specifi c cause can be found.
Given enough time, this patient volunteers a history of
pain in the frontal part of her neck and fl u-like symptoms
six months ago for which she had not sought medical
help. These unusual symptoms alert the physician to the
possibility of thyroiditis and consecutive hypothyroid-
ism, which was corroborated later. The graph illustrates
the vast array of pieces of potentially useful information.
Only small areas can be covered with direct active ques-
tioning or searching, as shown in the graph for vital signs,
symptoms of depression and medication that can cause
tiredness. In the example presented here, these are all
negative. However, foraging under guidance of the
patient leads the clinician to a very rare complaint that
triggers specifi c investigations. Premature switching to a
question-and-answer-mode would have resulted in a
longer and less focused process, which would have
delayed defi nite diagnosis considerably.
Few studies have investigated diagnostic reasoning
and decision making in real practice. Little attention
has been given to the earlier stage of patient-physician
physicians have arrived at their fi rst hypothesis, further
information provided by the patient is seen in a (dis-)
confi rmatory light, i.e. whether or not the information
is relevant to the hypothesis entertained by the practi-
tioner. A large amount of information can be discarded
as not contributing. A messy picture suddenly looks
ordered. However, at this early stage there is a risk of
too greatly reducing the range of possible explanations.
To conclude that relevant diagnoses have been excluded
with acceptable probability, problem areas must be
explored suffi ciently. The order in which this should hap-
pen is best left to the patient. Given enough time, they
will lead the clinician like a sniff er dog on a leash (Anon-
ymous GP, Basle [Switzerland]. Personal Communication.
2009) to areas where information can be found.
The effi ciency of inductive foraging as a strategy of data
acquisition is illustrated by the case of a 52-year-old
female patient presenting with tiredness of three
months duration (Figure 2). A vast number of diseases
can cause the symptom. Among these, defi ned somatic
aetiologies are rare. Psychological disorders are more
52 year old woman
with tiredness
Vital signs?
Criteria for depression?
Medication causing
Dry skin
Neck pain and flu-like
illness 6 months ago
Figure 2. Case of a 52 year old woman presenting with tiredness. Graph shows space of potentially relevant information from history, physical signs
and further investigations. ‘ 0 ’ , normal; ‘ 1 ’ , abnormal nding; grey rectangles, information actively asked for routinely.
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Inductive foraging 73
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encounters. By defi nition, this stage is unstructured,
and one cannot easily formulate specifi c rational strat-
egies of inquiry. Moreover, the opening stage of an
encounter depends on the context that cannot be cap-
tured by in vitro studies based on paper cases or stan-
dardized patients. Therefore, future research should
explore the dynamics of the inductive foraging stage
of the consultation, exploratory tactics used by clini-
cians, the responses they elicit from their patients, and
whether these are associated with measures of diag-
nostic success.
Health professionals need to be aware of the existence
and value of the inductive foraging stage described
above. They should realize that giving patients suffi cient
time to elaborate on their complaints not only eases the
patients sense of distress (25), but is also likely to
improve the diagnostic outcome of the consultation.
Closed questions referring to the presence or absence of
specifi c symptoms should be reserved for the deductive
enquiry stage. Instead, open questions encouraging fur-
ther exploration and elaboration should be asked, if
needed: How did it start? Have you noticed anything
else? What else is diff erent from usual? What about your
everyday activities? With these kinds of questions clini-
cians will also be able to move the discourse back to
inductive foraging if premature closure has occurred by
the patient. At the same time, clinicians should pay
attention to their sense that perhaps something is not
The considerations referring to inductive foraging are
particularly relevant for the care of unselected popula-
tions, i.e. primary care or emergency department hospi-
tal settings (26). Here, complaints are often non-specifi c,
and a large number of possible diagnoses must be
screened; inductive foraging may be the most effi cient
way to achieve this. Prematurely advancing to hypothe-
sis-guided deductive inquiry would inappropriately
restrict the scope of possible explanations.
Hopefully, the concept of inductive foraging will not
only have a descriptive value, but will also encourage
physicians, teachers and students to refl ect on how their
diagnostic ideas arise. They will fi nd that there is not
necessarily a trade-off between patient-centred commu-
nication and eff ective diagnosis, because skilful induc-
tive foraging can improve both.
Declaration of Interest: The authors report no confl icts
of interest. The authors alone are responsible for the
content and writing of the paper.
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Journal ArticleDOI
Daniel Kahneman1, Dale T. MillerInstitutions (1)
Abstract: A theory of norms and normality is presented and applied to some phenomena of emotional responses, social judgment, and conversations about causes. Norms are assumed to be constructed ad hoc by recruiting specific representations. Category norms are derived by recruiting exemplars. Specific objects or events generate their own norms by retrieval of similar experiences stored in memory or by construction of counterfactual alternatives. The normality of a stimulus is evaluated by comparing it to the norms that it evokes after the fact, rather than to precomputed expectations. Norm theory is applied in analyses of the enhanced emotional response to events that have abnormal causes, of the generation of predictions and inferences from observations of behavior, and of the role of norms in causal questions and answers. This article is concerned with category norms that represent knowledge of concepts and with stimulus norms that govern comparative judgments and designate experiences as surprising. In the tradition of adaptation level theory (Appley, 1971; Helson, 1964), the concept of norm is applied to events that range in complexity from single visual displays to social interactions. We first propose a model of an activation process that produces norms, then explore the role of norms in social cognition. The central idea of the present treatment is that norms are computed after the event rather than in advance. We sketch a supplement to the generally accepted idea that events in the stream of experience are interpreted and evaluated by consulting precomputed schemas and frames of reference. The view developed here is that each stimulus selectively recruits its own alternatives (Garner, 1962, 1970) and is interpreted in a rich context of remembered and constructed representations of what it could have been, might have been, or should have been. Thus, each event brings its own frame of reference into being. We also explore the idea that knowledge of categories (e.g., "encounters with Jim") can be derived on-line by selectively evoking stored representations of discrete episodes and exemplars. The present model assumes that a number of representations can be recruited in parallel, by either a stimulus event or an

2,748 citations

Book ChapterDOI
Abstract: This paper introduces a theoretical framework that describes the importance of affect in guiding judgments and decisions. As used here, “affect” means the specific quality of “goodness” or “badness” (i) experienced as a feeling state (with or without consciousness) and (ii) demarcating a positive or negative quality of a stimulus. Affective responses occur rapidly and automatically—note how quickly you sense the feelings associated with the stimulus word “treasure” or the word “hate”. We argue that reliance on such feelings can be characterized as “the affect heuristic”. In this paper we trace the development of the affect heuristic across a variety of research paths followed by ourselves and many others. We also discuss some of the important practical implications resulting from ways that this heuristic impacts our daily lives.

2,135 citations

Journal ArticleDOI
Joshua Klayman1, Young Won HaInstitutions (1)
Abstract: Strategies for hypothesis testing in scientific investigation and everyday reasoning have interested both psychologists and philosophers. A number of these scholars stress the importance of disconfir. marion in reasoning and suggest that people are instead prone to a general deleterious "confirmation bias" In particula~ it is suggested that people tend to test those cases that have the best chance of verifying current beliefs rather than those that have the best chance of falsifying them. We show, howeve~ that many phenomena labeled "confirmation bias" are better understood in terms of a general positive test strate~. With this strategy, there is a tendency to test cases that are expected (or known) to have the property of interest rather than those expected (or known) to lack that property. This strategy is not equivalent to confirmation bias in the first sense; we show that the positive test strategy can be a very good heuristic for determining the truth or falsity of a hypothesis under realistic conditions~ It can, howeve~ lead to systematic errors or inefficiencies. The appropriateness of human hypotheses-testing strategies and prescriptions about optimal strategies must he understood in terms of the interaction between the strategy and the task at hand.

1,737 citations

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