Statistical issues in the analysis of low-dose endocrine disruptor data

The National Institute of Environmental Health Sciences (NIEHS) and the U,S, Environmental Protection Agency (U.S. EPA) recently cosponsored the Endocrine Disrupters Low-Dose Peer Review. The purpose of this meeting was to examine data supporting the presence or absence of low-dose effects of endocrine disrupters in specific studies and then to evaluate the likelihood and significance of these and/or other potential low-dose effects for humans. All invited speakers agreed to provide their raw data in advance of the meeting to a Statistics Subpanel, which was asked to reevaluate the authors' experimental design, data analysis, and interpretation of experimental results, The purpose of this statistical reevaluation was to provide an independent assessment of the experimental design and data analysis used in each of the studies and to identify key statistical issues relevant to the evaluation and interpretation of the data. This paper presents a summary of the Statistics Subpanel's evaluation. Specific examples are presented to illustrate problems that arose in the experimental design and data analysis of certain studies, The statistical principles and issues that are discussed in this paper are not unique to endocrine disrupter studies and should provide important guidelines regarding appropriate experimental design and statistical analysis for other types of laboratory investigations.