Pathology and probability. Likelihood ratios and receiver operating characteristic curves in the interpretation of bronchial brush specimens.

Diagnoses in pathology often are qualitative, such as atypical or suspicious, and consequently are thought to have limited clinical value. To investigate the utility of a qualitative diagnostic system, seven pathologists retrospectively evaluated 100 bronchial brush specimens using the following categories: definitely benign, probably benign, possibly malignant, probably malignant, and definitely malignant. The likelihood ratio (LR) and receiver operating characteristic (ROC) curve, two statistical probabilistic measurements, were used to calculate diagnostic accuracy among individuals and groups. The results show: (1) the LR for individual diagnostic categories varied among observers, resulting in different clinically malignant probabilities; (2) observer experience did not appear to play a role in overall diagnostic accuracy, except in the diagnosis of small cell carcinoma; (3) observers operate at higher levels of diagnostic accuracy with, rather than without, clinical history. The authors conclude that qualitative diagnoses contain important information and can be interpreted effectively with LR and ROC.