ABSTRACT
This chapter discusses the books and papers that appeared in the mid-to-late 20th century, after the very public arguments over mathematical correlation and its coefficient had ended. Almost all statistical textbooks were being written by mathematicians or mathematically trained statisticians. The first two books solely on the topic of correlation were published. Correlation was now being used to analyze clinical trials data. The method for calculating the coefficient of curvilinear correlation (i.e., the correlation ratio) was much improved. The authors still struggled to explain correlation in words (most authors preferred to explain it with only a formula). At the end of the century, authors began to use Venn diagrams and p-values to explain correlation. The question of whether correlation is best measured using the coefficient of determination or the correlation coefficient had yet to be answered, at least in the minds of some textbook authors.
