Activity of xenoestrogens at nanomolar concentrations in the E-Screen assay

Our studies illustrate the difficulties that may be encountered during the estimation of low doses in vivo. High statistical power is required when the underlying dose-response curves are shallow. Through the use of large sample sizes and numerous repeats, the experimental power of the E-Screen assay was sufficiently high to measure effect magnitudes of around 1-2% with reliability. However, such resources are usually not available for in vivo testing, with the consequence that the statistical detection limits are considerably higher. If this coincides with shallow dose-response curves in the low-effect range (which is normally not measurable in vivo), the limited resolving power of in vivo assays may seriously constrain low-dose testing