Bayesian Reasoning in Medical Contexts — Practice

Practice bank for UCAT Decision Making questions involving Bayesian/diagnostic reasoning.

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Quick-Reference: Diagnostic Test Measures

Key Definitions

Measure	Definition	Formula
Sensitivity	P(positive test | disease)	True positives / (True positives + False negatives)
Specificity	P(negative test | no disease)	True negatives / (True negatives + False positives)
PPV	P(disease | positive test)	True positives / (True positives + False positives)
NPV	P(no disease | negative test)	True negatives / (True negatives + False negatives)
Prevalence	P(disease)	Total with disease / Total population

The 2×2 Table Method

	Disease +	Disease −	Total
Test +	True Positive (TP)	False Positive (FP)	TP + FP
Test −	False Negative (FN)	True Negative (TN)	FN + TN
Total	TP + FN	FP + TN	N

Step-by-Step for UCAT