"Quantifying the precision of ecological risk: Misunderstandings and errors in the methods for assessment factors versus species sensitivity distributions".

Belanger, Scott E; Carr, Gregory J

The science of species sensitivity distributions (SSDs) is a blend of statistical theory, ecotoxicological testing, study reliability, and biodiversity. The utility of SSDs has been well reviewed and they are viewed as a high tier assessment tool in environmental risk assessment and other disciplines. SSDs seek to improve upon probabilistic extrapolation of laboratory (and sometimes field) collected ecotoxicity data for environmental protection by modeling the diversity of multiple experimental results in the form of a single statistical distribution which reduces or eliminates the need for extrapolation with deterministic assessment factors. SSDs thus depend heavily on both statistical and biological knowledge. In this commentary we review recently published literature identifying areas of improvement based on fundamental statistical theory or application in environmental assessment contexts. We reveal that sound application of SSDs relies heavily upon a grasp of probability distributions, how asymmetric confidence intervals are derived for distributions common to SSDs, the influence of sample size on parameter estimation, and how these are collectively applied across the myriad of regulatory systems globally. Statisticians and ecotoxicologists are inextricably bound together in the goal of actually improving hazard assessment using both probabilistic and deterministic methodologies.