Researchers do studies that show e.g. that drinking coffee in the afternoon has a significant effect on sleep (let's say it results in an average of 15 minutes

Researchers do studies that show e.g. that drinking coffee in the afternoon has a significant effect on sleep (let's say it results in an average of 15 minutes less sleep, p < 0.05). This is valuable information, but people are different, so the question is, to what extent does this apply to me? Genetics might help predict this (rs762551 ?), but in practice I'll just need to test this for myself. The notion that there aren't always one-size-fits-all solutions is well accepted (though often still not well implemented) in medicine (a.k.a. personalized medicine).