If you're interested in this type of study this is the name of the method: https://en.wikipedia.org/wiki/Mendelian_randomization https://en.wikipedia.org/wiki/M

If you're interested in this type of study this is the name of the method: https://en.wikipedia.org/wiki/Mendelian_randomization https://en.wikipedia.org/wiki/Mendelian_randomization When I just read the article I glad to see the method I learned during my thesis has produced some mainstream knowledge. Happy to see that! It's basically "nature's randomized control trial" since you assume genes to be assigned randomly. The treatment and control group just vary in terms of this one set of SNPs, which are used as instrumental variables. In this case, comparing a genetic population of nappers to one of non-nappers. They don't have to measure their actual nap time because the genetics serve as proxy.