I suggest anyone doubting the importance of eliminating all differences between the experimental cohort and the control group to read that speech from Feynman:

I suggest anyone doubting the importance of eliminating all differences between the experimental cohort and the control group to read that speech from Feynman: https://calteches.library.caltech.edu/51/2/CargoCult.htm https://calteches.library.caltech.edu/51/2/CargoCult.htm or this article that highlights it's most important part: https://www.realclearscience.com/blog/2014/02/the_rat_experiment_you_dont_know_about_but_should.html https://www.realclearscience.com/blog/2014/02/the_rat_experi... . If I had to reduce that to some phrases I would say : the easiest way to do bad science is to lie to yourself, so to do good science you must foremost learn how not to do that. And avoiding avoidable difference in cohorts is one of the first step to stay honest.