Note 4 — Chapter I
Reading edition
What is said here refers to positive correlations, which are the only kind involved in this problem. Correlations may also be negative, lying between 0 and -1; for instance, if we measured the correlation between a man's lack of appetite and the time that had elapsed since his last meal, we would have to express it by a negative fraction, the minus sign showing that the greater his satiety, the less would be the time since his repast. The best introduction to correlations is Elderton's Primer of Statistics (London, 1912).