Flexible and efficient though diagnostic reasoning may be, it is subject to a number of errors that are a consequence of the fact that the human computer has inherent capacity limitations and is vulnerable to interference by intrinsic and extrinsic factors.
The diagnostician’s judgment can be clouded by fatigue or illness. Clinical judgment can also be biased when the clinician has an emotional reaction to the patient based, for example, on unresolved conflict from his or her own childhood experience (ie, countertransference).
As mentioned earlier in this chapter, no more than four to six diagnostic hypotheses can be juggled at one time because the capacity of short-term memory is limited. This limitation is even more evident in the case of dynamic hypotheses, in which case the clinician will often be satisfied with a single hypothesis, failing to consider alternatives.
The human computer is more impressed by information and hypotheses that appear early in the diagnostic encounter and is relatively less efficient at accounting for later data, especially if the data run counter to first impressions. However, the expert clinician is able to adjust initial hypotheses in response to new information and to drop them when they no longer fit. Expert radiologists, for example, know where to look, what to see, and how to frame an anomalous pattern conceptually. They then engage in “top-down, bottom-up” recursive thinking, testing their initial flexible hypotheses against the details of the radiologic film and progressively adjusting or discarding their hypotheses in accordance with the evidence.
In the same way, the expert psychiatrist quickly discerns significant cues, makes tentative inferences, and assembles a dynamic pattern that allows efficient hypothesis generation. From these hypotheses, he or she begins recursive hypothesis testing, seeking both standard and discretionary data. Table 9-4 lists the chief potential flaws in this process.