ABSTRACT
This chapter describes Pearson's (1896) product moment correlation which assesses the strength, direction and probability of the linear association between two interval or ratio variables. Tests for determining whether Pearson's correlations differ for variables which come from the same or different samples are also discussed. We would use these tests to find out, for example, whether the correlation between the pre-test and post-test marks is similar to that between the post-test and follow-up marks for the sample, or whether the correlation between pre-test and post-test marks is similar for women and men. In addition, Pearson's partial correlation which covaries out the effects of one or more variables that may be related to the two variables of interest is covered, as is eta which provides an index of the non-linear association between an interval/ratio variable and a categorical/ordinal one.
