I just read that at an experiment some rats weighed almost 3 times as much as the lightest rat. (!!!) I have never seen a paper that said "rats of near equal mass" Imagine giving a drug to a human of 35Kg, 70Kg, and 105Kg, you would get noticeably different effects. Thus I think that when they do mammal experiments they should specify near equal mass mammals. This could provide much better data.
here is an image of an older experiment that describes different rat masses:
some rats weigh almost three times as much others.png 14.71KB 3 downloads
Edited by treonsverdery, 02 March 2017 - 02:40 AM.