Pitfalls In Decisions
About Diagnosis And Prescribing
mistakes. But our reliance on cognitive processes prone
to bias makes treatment errors more likely than we think
Psychologists have studied the cognitive processes involved
in decision making extensively and have identified many
factors that lead people astray. Because doctors' decisions
have profound effects on their patients' health, these
decisions should be of the best possible quality. All
doctors should therefore be aware of possible pitfalls
in medical decision making and take steps to avoid
these unnecessary errors. Presented here are five examples of
cognitive biases that can affect medical decision making
and offer suggestions for avoiding them.
of decision making
Doctors often have to make rapid decisions, either because of
medical emergency or because they need to see many patients
in a limited time. Psychologists have shown that rapid decision
making is aided by heuristicsstrategies that provide
shortcuts to quick decisionsbut they have also noted
that these heuristics frequently mislead us.1
Good decision making is further impeded by the fact
that we often fall prey to various cognitive biases.
correct decisions in clinical practice, doctors must first
gather information on which to base their judgments. According
to decision making experts Russo and Schoemaker,2
the best way to do this is to ask the most appropriate
questions, to interpret answers properly, and to
decide when to quit searching further. Straightforward
though this sounds, misleading heuristics and cognitive
biases create pitfalls throughout this process.
may believe that, as highly trained professionals, they
are immune to these pitfalls. Unfortunately, they are
just as prone to errors in decision making as anyone
Even worse, it is common for people who are particularly
prone to cognitive biases to believe that they are
good decision makers.2 As Shakespeare
put it, "The fool doth think he is wise, but the wise
man knows himself to be a fool." Studies based on
both simulated cases and questionnaires show that
doctors are susceptible to decision making biases,6
7 including insensitivity to known
a failure to consider other options, the attraction
effect, and the availability heuristic. The good news
is that training in these dangers can reduce the probability
of flawed medical decision making.
Pitfall 1: the representativeness heuristic
The representativeness heuristic is the assumption that something
that seems similar to other things in a certain category
is itself a member of that category. Kahneman and Tversky
showed this heuristic in a classic experiment in which
they presented participants with descriptions of people
who came from a fictitious group of 30 engineers and
70 lawyers (or vice versa).8 The
participants then rated the probability that the person
described was an engineer. Their judgments were much
more affected by the extent to which the description
corresponded to the stereotype of an engineer (for
example, "Jack is conservative and careful") than by
base rate information (only 30% were engineers), showing
that representativeness had a greater effect on the judgments
than did knowledge of the probabilities.
heuristic has also been shown in nursing. Nurses
were given two fictitious scenarios of patients with symptoms
suggestive of either a heart attack or a stroke and asked
to provide a diagnosis.9 The
heart attack scenario sometimes included the additional
information that the patient had recently been dismissed
from his job, and the stroke scenario sometimes included
the information that the patient's breath smelt of alcohol.
The additional information had a highly significant effect
on the diagnosis and made it less likelyconsistent
with the representativeness heuristicthat the nurses
would attribute the symptoms to a serious physical cause.
The effect of the additional information was similar
for both qualified and student nurses, suggesting
that training had little effect on the extent to
which heuristics influenced diagnostic decisions.
we avoid being led astray by the representativeness heuristic?
The key is to be aware not only of the likelihood of
a particular event (such as a stroke) based on situational
information (such as alcohol on the breath), but also
how likely the event is in the absence of that information.
In other words, it is important to be aware of base
rates of the occurrence of a particular condition
and to avoid giving too much weight to one piece
of information. By the same token, if a disease is
extremely rare, it may still be unlikely to be the correct
diagnosis even if a patient has the signs and symptoms
of that disease.
2: the availability heuristic
When we use the availability heuristic, we place particular
weight on examples of things that come to mind easily, perhaps
because they are easily remembered or recently encountered.
In general, this guides us in the right direction, as things
that come to mind easily are likely to be common, but it
may also mislead. The availability heuristic is apparent
after a major train crash, when some people choose
to travel by car instead of by rail, in the incorrect
belief that it is safer.
medical setting, one study asked doctors to judge the probability
that medical inpatients had bacteraemia. The probability
was judged to be significantly higher when doctors had
recent experience of caring for patients with bacteraemia.10
Another example is the documented tendency of doctors
to overestimate the risk of addiction when prescribing
opioid analgesics for pain relief and to undertreat
severe pain as a result.11-13
Risk of addiction is actually low when patients receive opioids
(particularly controlled release formulations) for pain,14
15 but opiate addiction tends to
receive high publicity and sothrough the availability
heuristicits likelihood may be overestimated.
falling prey to the availability heuristic, doctors should
try to be aware of all the diverse factors that influence
a decision or diagnosis. They should ask if their decision
is influenced by any salient pieces of information
and, if so, whether these pieces of information are
truly representative or simply reflect recent or
otherwise particularly memorable experiences. Knowing
whether information is truly relevant, rather than
simply easily available, is the key.
for good decision making
aware of base rates
whether data are truly relevant, rather
than just salient
reasons why your decisions may be wrong
and entertain alternative hypotheses
questions that would disprove, rather than confirm,
your current hypothesis
that you are wrong more often than
To use our knowledge effectively, we must be aware of its limitations.
Unfortunately, most of us are poor at assessing the gaps
in our knowledge, tending to overestimate both how
much we know and how reliably we know it (see bmj.com
for an example). Research has shown that almost all
of us are more confident about our judgments than we
should be. Since medical diagnoses typically involve
some uncertainty, we know that almost all doctors make more
mistakes in diagnosis than they think they do. Overconfidence
also comes into play when doctors rate their clinical skills.
Larue et al found that both primary care doctors and medical
oncologists rated their ability to manage pain highly, even
though they actually had serious shortcomings in their attitudes
toward and knowledge of pain control.16
of overconfidence are obvious. Doctors who overestimate
their management of a condition may continue to prescribe
suboptimal treatment, unaware that their management
could be improved. Also, overconfidence in diagnostic
abilities may result in too hasty a diagnosis, when
further tests are needed. It is critical, therefore,
to be aware of the limits of your knowledge and to ensure
that knowledge is kept up to date. Awareness of your shortcomings
makes it more likely that you will gather further information.
It can also be helpful to make a habit of seeking the
opinions of colleagues.17
Pitfall 4: confirmatory bias
Confirmatory bias is the tendency to look for, notice, and remember
information that fits with our pre-existing expectations.
Similarly, information that contradicts those expectations
may be ignored or dismissed as unimportant.1
2 Confirmatory bias has been shown
to affect peer-reviewers' assessments of manuscripts. Mahoney
sent fictitious manuscripts with identical methods but different
results to reviewers.18
Reviewers gave significantly better ratings to the
methods section when the results supported their pre-existing
doctors are not immune to confirmatory bias. In taking
medical histories, doctors often ask questions that solicit
information confirming early judgments. Even worse, they
may stop asking questions because they reach an early
conclusion, thus failing to unearth key data. More
generally, the interpretation of information obtained
towards the end of a medical work-up might be biased
by earlier judgments.19
bias can also lead to treatment errors. It is natural
to expect that the drug you are about to administer is
the correct drug. Apparently obvious information that you
have the wrong drugfor example, a label marked ephedrine
instead of the expected epinephrinemay be ignored
or misinterpreted to confirm your expectation that
the drug is correct.20
Psychologists have extensively studied the cognitive
processes involved in making decisions
Heuristics and biases that lead to
poor decisions are widespread, even among doctors
Awareness of the cognitive processes
used to make decisions can reduce the
likelihood of poor decisions
the danger of confirmatory bias is greatest when making
decisions about diagnosis, ongoing treatment decisions
are also affected. It is thus critical to remain
constantly vigilant for any information that may
contradict your existing diagnosis, and to give any
such information careful consideration, rather than
dismissing it as irrelevant. It is also a good idea to
try to think of specific reasons why your current theory
might be wrong and to ask questions that could potentially
disprove your hypothesis. Always be aware of alternative
hypotheses and ask yourself whether they may be better
than your current ideas.
Pitfall 5: illusory correlation
Illusory correlation is the tendency to perceive two events
as causally related, when in fact the connection between
them is coincidental or even non-existent. (It has
some overlap with confirmatory bias when causes that
fit with pre-existing ideas are noticed.) Homoeopathy
provides an excellent example of illusory correlation.
Homoeopaths will often notice when patients improve after
being treated with a homoeopathic remedy and claim this as
evidence that homoeopathic treatment works. However, no convincing
evidence exists that homoeopathic treatments are effective.w12
w13 Illusory correlation is probably at work: homoeopaths
are likely to remember occasions when their patients
improve after treatment.
prey to illusory correlation can reinforce incorrect beliefs,
which in turn can lead to the persistence of suboptimal
practices. Ask yourself whether any instances do not fit
with your assumed correlations. A straightforward
way to do this is simply to keep written records
of events that you believe to be correlated, making
sure that all relevant instances are recorded.
Doctors often have to make decisions quickly. However, the greatest
obstacle to making correct decisions is seldom insufficient
time but distortions and biases in the way information is
gathered and assimilated. Being aware that decisions
can be biased is an important first step in overcoming
those biases. In real life, of course, biases may not
necessarily fit neatly into any one of the categories
I described above but may result from a complex interaction
of different factors. This increases the potential
for poor decisions still further. The good news is that
it is possible to train yourself to be vigilant for these
errors and to improve decision making as a result .
Jill G Klein
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