That error opens up onto the myriad conceptual fallacies built into the entire enterprise, if something so unavoidable can be called an “error.” Past performance is no guarantee of future results; but past performance is all a pollster has to go on. That’s why much of the process of choosing and weighting samples is … well, you can call it “more art than science.” Or you can call it “intuitive.” Or you can call it “trial and error.” But you can also call it “made up.”