HYPOTHESIS-TESTING WITH VALUES BELOW DETECTION LIMIT IN ENVIRONMENTAL-STUDIES

Values below a specified detection limit are a common occurrence in environmental measurement which complicates statistical analysis. This paper addresses the problem of how these data may be included in hypothesis testing and demonstrates a solution that uses a regression model in the SAS statistical package with the ability to accommodate left-censored data. To illustrate, the LIFER-EG procedure is applied to data for an analyte (tin) found in fish tissue during a multifactorial bioaccumulation study involving two experimental sites, three experiments at each site, and sampling on multiple days. The results of this analysis are presented, indicating evidence of bioaccumulation but no significant differences between sites or experiments. While regression methods to accommodate left-censored data are not new, their use in environmental studies does not appear to be widely practiced. The strengths and limitations of this approach are discussed.