Clinical Hypotheses MCQs

Occam razor favours a single unifying diagnosis that explains all findings. Hickam dictum is the counter-principle: patients can have several diseases at once, so a unifying diagnosis should not be forced when features do not fit.

Premature closure is accepting a diagnosis before it has been fully verified, closing off the differential too early. Anchoring is different: it is over-weighting the initial information even as new data arrives.

Anchoring bias occurs when clinicians cling to an initial diagnostic impression and adjust insufficiently in light of later findings. Countermeasures include deliberately generating alternatives and seeking disconfirming evidence.

By Bayes theorem, PPV = (0.90 x 0.10) / [(0.90 x 0.10) + (0.05 x 0.90)] = 0.09 / 0.135, about 0.67 or 67%. Even a good test yields many false positives when prevalence is low.

Sensitive tests have few false negatives, so a negative result reliably rules out disease (SnNout). Specific tests have few false positives, so a positive result rules in disease (SpPin).

Illness scripts are mental models of a disease: its predisposing conditions, pathophysiology, typical features and course. A clinical presentation activates the matching script, which is why experts diagnose rapidly from pattern recognition.

Availability bias is judging how likely something is by how easily examples come to mind. A recent, vivid or memorable case inflates the perceived probability of the same diagnosis in the next patient.

A test is valuable in proportion to how much it moves the probability of the leading hypothesis, which is captured by its likelihood ratios. The most discriminating test produces the largest shift in post-test probability.