Effect of outlying standard points on curve fitting in radioimmunoassay

Outlying points often appear in standard curves for radioimmunoassay. We have examined the effect of outlying standard points on the ability of various automated data-processing routines, and of manual operators, to position a radioimmunoassay standard curve correctly. Manual operators were found to be highly subjective in their handling of a standard curve containing outlying points. Automated methods without outlier rejection capability produced standard curves that were significantly erroneous. In contrast, a data-processing method with automated outlier rejection capability successfully identified outliers, but occasionally rejected valid points--and consequently misplaced the standard curve. Visual identification of outliers is unsatisfactory. Automated identification can be more satisfactory, but some patterns of outliers make it less so. We conclude that any automated data-processing method should contain an outlier rejection facility, but its results should be treated with caution.