[bayesianhorse]

One big difference is the cost of the studies. A study with 20-50 human participants would be orders of magnitudes more expensive than using rats.

But there just is no practical reason why this particular study lacks a control group or the statistical power to show its conclusion.

[jules]

Actually, in many countries it is really really hard to be allowed to do a study on a significant amount of animals due to animal rights groups, which have lobbied for committees who decide how many animals are allowed. Most times this number is way too low to do good science (numbers like 16 -- 8 main and 8 control mice, are not uncommon).