The calculation of historical control limits in toxicology: Do's, don'ts and open issues from a statistical perspective.

For reporting toxicology studies, the presentation of historical control data and the validation of the concurrent control group with respect to historical control limits have become requirements. However, many regulatory guidelines fail to define how such limits should be calculated and what kind of target value(s) they should cover. Hence, this manuscript is aimed to give a brief review on the methods for the calculation of historical control limits that are in use as well as on their theoretical background. Furthermore, this manuscript is aimed to identify open issues for the use of historical control limits that need to be discussed by the community. It seems that, even after 40 years of discussion, more issues remain open than solved, both, with regard to the available methodology as well as its implementation in user-friendly software. Since several of these topics equally apply to several research fields, this manuscript is addressed to all relevant stakeholders who deal with historical control data obtained from toxicological studies, regardless of their background or field of research.