Number of studies reporting animal numbers in the methods and results sections.

†4% (12/271) of all included studies had no record of animal numbers in either the methods or results sections. Note: Studies were assessed according to whether the exact number of animals used was reported (e.g. 50 rats divided into 5 treatment groups comprising 10 rats each), the number of animals could be estimated (e.g. 50 rats divided into 5 groups or treatments comprised 8–12 rats) or the number of animals was not clearly stated (e.g. treatments were applied to 5 groups of rats).