Formulas are presented for triserial correlation, quadriserial correlation, etc., and for serial correlation in general. These formulas are based on well-known procedures outlined by Kelley, Peters and Van Voorhis, and others, and involve Pearson's correction for “broad categories.” The formula for biserial correlation also may be developed following these procedures. The assumptions underlying serial correlation are that the segmented variable is basically continuous and normally distributed, and that all the segments which together would form a whole normal distribution are present.