The FREQ Procedure

The SENSPEC option in the TABLES statement provides estimates of sensitivity, specificity, positive predictive value, and negative predictive value for tables. These measures are conditional (row and column) proportions in the table crosstabulation. In sensitivity analysis, the row variable might represent a positive or negative diagnostic test result, and the column variable might represent the presence or absence of a condition. For more information, see Fleiss, Levin, and Paik (2003).

Sensitivity is defined as the column proportion for table cell (1,1), which is the ratio of the frequency in table cell (1,1) to the total frequency in column 1 of the table. The estimate of sensitivity is computed as

Specificity is defined as the column proportion for table cell (2,2), which is the ratio of the frequency in table cell (2,2) to the total frequency in column 2. The estimate of specificity is computed as

The positive predictive value is the row proportion for table cell (1,1), which is computed as

The negative predictive value is the row proportion for table cell (2,2), which is computed as

The "Sensitivity and Specificity" table provides the estimates together with their standard errors and Wald confidence limits. PROC FREQ computes the standard errors and Wald confidence limits for these proportions as described in the section Risks and Risk Differences. The value of the confidence coefficient is determined by the ALPHA= option; by default, ALPHA=0.05, which produces 95% confidence limits.