For most of us, mathematics is a pain in the neck, and we avoid it whenever we can. We hire an expert to figure our tax. We trust the clerk to make the right change. We buy meat weighed on a computing scale and gasoline from a computing pump. We learned algebra in school, but we've forgotten it! What wonder that most of us neither use nor understand the mathematics of statistics, which deals with general tendencies and random differences. We'd be glad to forget this, too, if we'd ever learned it. Or perhaps we wouldn't forget it, for there's a good likelihood that we'd find frequent occasion to use it, which is certainly not true of algebra. Statistics deal with chances. It attempts to tell, from looking at a few patients, what one could expect in 100 or 10,000—from making a few measurements, what they would be if one hundred times repeated. Chances indicate the number of times one would encounter this or that in a large population. For me chances have no meaning unless there exists in reality, or in my i...