Every dataset I've ever received came with a description. Almost none of them matched the data. Not because anyone was lying. The person who wrote the README usually described the dataset as it was supposed to be, or as it was six months ago. The data itself has been quietly drifting since then. So before I compute a single mean, I run the same short ritual. It takes five minutes and has saved me from shipping wrong conclusions more times than I can count. 1. Count the nulls,...