There are a couple studies with good methodology on penis length, but not many. I would be suspicious of older studies since racism led at least some older studies to inflate the "measurements" for members of some races and deflate them for others. There are also a lot of studies that rely on self reporting which is also unreliable for obvious reasons. That's why I am only aware of two reputable studies. I'd take this particular meta analysis with more than just a grain of salt