ABSTRACT

In 1914 the psychologist Thorndike selected the lowercase letter r as the symbol for what he called the median of certain specialized ratios, a quan­ tity that happened to equal what is now called Pearsonian sample correla­ tion. In keeping with today’s convention that codes variates as uppercase Latin letters which occur towards the end of the alphabet, it would have been a stroke of good luck if either Thorndike or Pearson had called upon the capital letter R, rather than r, to denote the most popular estimator of the parameter that is now denoted by the Greek letter p. Yet, at least when compared to some other tortuous notational pathways, the history of r is straightforward.