A FURTHER REFINEMENT OF THE RELIABLE CHANGE (RC) INDEX BY IMPROVING THE PRE-POST DIFFERENCE SCORE - INTRODUCING RCID

The development of methods for demonstrating clinical (in addition to statistical) significance has been referred to as one of the major adv ances in outcome research. In a recent article, Speer (1992; Journal o f Consulting and Clinical Psychology, 60, 402-408) suggested that the Reliable Change (RC) Index neglects possible confounding of improvemen t rate estimates by regression to the mean, to which latter's existenc e he concludes when a negative correlation between initial score and a mount of change is observed. Speer (1992) proposed an alternative meth od that incorporates an adjustment which minimizes this confound when statistical regression has been empirically shown to be present. In th e present paper, it is argued that both the rationale for arriving at this alternative method and the method itself are erroneous. Introduci ng RC(ID) the present authors provide a modification and refinement of the RC Index by improving the pre-post difference score, taking into account regression to the mean due to measurement unreliability. Furth er advantages of the RC(ID) Index are briefly discussed.