| Abstract: | The techniques of matched groups, analysis of covariance, and partial correlation represent various approaches to the prevention of a spurious association between X1 and X2 due to a confounding variable, X3. In all these techniques the use of an unreliable measure for X3 leads to a systematic bias of undercorrection. Adequate corrections are possible for the case of known reliability of X3. Groups should be matched on true scores rather than observed scores, but no correction is possible for the factorial design in which groups are formed on the basis of unreliable correlated measures. Partial correlations should be corrected for the effects of unreliability of the controlled variable. Spuriously high partials are usually obtained when this correction is not applied. (PsycINFO Database Record (c) 2010 APA, all rights reserved) |
