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The aerobic power of 41 male and 29 female introductory psychology students was measured. They were then subjected to a series of psychosocial stressors. Tonic heart rate was used as the criterion variable. Aerobic power was found to be significantly (p < .001) related to how quickly subjects recovered from stress.

ANCOVA and regression both exhibit a directional bias when measuring correlates of change. This bias confounds the comparison of changes between naturally occurring groups with large pretest differences (ANCOVA), or for identifying predictors of change when the predictor is correlated with pretest (regression). This bias is described in some detail. A computer simulation study is presented, which shows that properly identified structural equation models are not susceptible to this bias. Neither gain scores (posttest minus pretest) nor structural equation models exhibit the “regression bias.” Other factors, such as skewness, that may confound measurement of change are also discussed.