Medical Diagnostic Tests: A Review of Test Anatomy, Phases, and Statistical Treatment of Data

Table 9

Other metrics used to evaluate diagnosis accuracy.

Statistic (Abb)	Formula	Remarks
Number needed to diagnose (NND) [161]	1/[Se − (1 − Sp)]1/J	(i) The number of patients that need to be tested to give one correct positive test result; (ii) Used to compare the costs of different tests
Number needed to misdiagnose (NNM) [162]	1/[1 − (TP + TN)/n]	(i) The highest the NNM, the better the diagnostic test
Clinical utility index (CUI) [163, 164]	CUI+ = Se × PPV; CUI− = Sp × NPV	(i) Gives the degree to which a diagnostic test is useful in clinical practice; (ii) Interpretation: CUI > 0.81 ⟶ excellent utility; 0.64 ≤ CUI < 0.81 ⟶ good utility; 0.49 ≤ CUI < 0.64 ⟶ fair utility; 0.36 ≤ CUI < 0.49 ⟶ poor utility; and CUI < 0.36 ⟶ very poor utility

Abb = abbreviation; all indicators excepting J are reported with associated 95% confidence intervals; TP = true positive; FP = false positive; FN = false negative; and TN = true negative.