A NOVEL STATISTICAL APPROACH FOR THE COMPARISON OF ANALYTICAL METHODSTO MEASURE ANGIOTENSIN-CONVERTING ENZYME-ACTIVITY, ENALAPRILAT, AND BENAZEPRILAT

Two different analytical techniques were used to measure angiotensin c onverting enzyme (ACE) activity, and three different methods were used to measure each of the ACE inhibitors enalaprilat and benazeprilat. A ll measurements were made in human plasma. The groups of methods were compared by two different statistical approaches. First, the means of the methods were compared by the paired ttest or analysis of variance, depending on whether two or three different methods were under compar ison. Second, the squared coefficients of variation of the methods wer e compared by the Jackknife technique. The dual statistical approach e mployed enabled both the accuracy and the variability of the analytica l methods to be compared and is a superior approach to the inappropria te use of correlation coefficients that are commonly used to compare a nalytical techniques. No statistically significant difference was foun d between the two assays used to measure ACE activity. Differences wer e found between the three methods to measure enalaprilat, although no obvious reason could be found for this phenomenon. Significant differe nces were also found between the three methods used to measure benazep rilat and were attributed to the presence of metabolites interfering i n the nonspecific assay methods.