The data in Table 8.5 are a subset of the data considered by Clark, Vandenberg, and Proctor (1961) in a study concerned with the relationship of scores on various psychological tests and certain physical characteristics of twins. Table 8.5 gives the test scores (totals of a number of different psychological tests) of 13 dizygous (i.e., non-identical) male twins. Test the hypothesis of independence versus the alternative that the twins' test scores are positively correlated.
