Corrections For Spurious Influences On Correlations Between Mmpi Scales

Correlations between measures containing common elements have a spurious component due to the overlapping elements. For example, personality scales such as the MMPI and the CPI have subscales with overlapping items, so correlations between these subscales are spuriously influenced by this overlap. Methods for statistical and experimental adjustment of these spuriously influenced correlations are reviewed and compared, but are rejected in favor of Bashaw and Anderson's (1967) reliability solution. To illustrate the proposed correction and to show the potential magnitude of this spurious influence, the original "Minnesota normals" data on nine clinical subscales of the MMPI were analyzed. A comparison of the unadjusted and adjusted values showed that 32 of the 36 correlations were changed, six of them were radically changed, and in two cases the sign of the correlation was reversed. A principal components analysis was used to investigate changes in the correlation structure.