Make decisions with scalar parameters.

Find a number that will drive the decision using clear theory, even if the theory has to be strong. Never try to make a decision from multiple variables. Data analysis is about reducing the data to a number that tells you what you want to know. Don't stop a little short and use hand-waving to "balance" multiple parameters. Have good — or good enough — reasons for the parameter. But choose one.

(This is a note for my future self who will undoubtedly forget and relearn this lesson.)