Use of the Simple Change Score in Correlational Analyses'

This article examines the simple difference score (Y-X) as used in three different correlational analyses. As discussed in this paper, this difference score is viewed as a simple change from a pretest (X) to a posttest (1Y), but the generalizations apply to any difference score of the type (Y-X). The three classes of correlational analyses considered involve the correlation of initial score (X) with change (Y-X); the correlation of another variable (A) with change (Y-X); and the correlation of one change score (B-A) with another (Y-X). In each case, the complexity of the change score and the ambiguity of the resulting correlation are demonstrated. It is proposed that attention should be directed to the elements making up each correlation in addition to attempting to use and interpret the correlation itself.