Correlation of EIA and RIA. The results of the RIA and EIA were compared by linear regression analysis. There was a good correlation between the two methods, with a correlation coefficient of 0.974 and a P value of ,0.0001. The slope was 0.915,
and the intercept was 20.013 (Fig. 2). The RIA system had a greater range of results, with the highest result being 27.0 units.In contrast, for the same urine sample the result was 20.1 units by the EIA (Fig. 1).