CALIBRATION AND ASSAY DEVELOPMENT USING THE 4-PARAMETER LOGISTIC MODEL

Calibration and assay development using the four-parameter logistic model are described and illustrated with examples from radioimmunoassay (RIA) and enzyme linked immunosorbent assay (ELISA). Measures of assay performance including the minimum detectable concentration (MDC), the reliable detection limit (RDL), the limit of quantitation (LOQ), the precision profile and model goodness of fit, are defined and discussed. Assay quality control (QC) procedures for the working chemist are also presented. Both constant and non-constant variability in the calibration model response are considered. Estimation and evaluation of the response-error relationship (RER) is approached via generalized least squares/variance function estimation (GLS/VFE). The choice of variance function is shown to be important in constructing prediction limits and calculating measures of assay performance such as the MDC, RDL and precision profile. S-PLUS functions for four-parameter logistic fitting, RER estimation, and assay performance and calibration calculations have been posted to statlib *.