A cautionary tale of two statistics: partial correlation and standardized partial regression.

Abstract

Partial correlation and standardized partial regression are widely used to control for other variables in cross-sectional and longitudinal studies. Two aspects of these statistics can radically alter the interpretation of data and so deserve attention. First, their sign will be opposite to that of the original zero-order correlation when this correlation is of the same sign as and smaller than the product of the other 2 correlations. Second, their size will be considerably larger than a weak zero-order correlation when either that correlation is positive and the product of the other 2 correlations is negative or that correlation is negative and the product of the other 2 correlations is positive. The first aspect is illustrated with data from J. M. Gottman and L. J. Krokoff (1989) on initial conflict behavior and initial and later marital satisfaction, and the 2nd aspect is illustrated with data from C. L. Heavey, C. Layne, and A. Christensen (1993) on the same issue. Their interpretation of their findings is questioned.