As highlighted in the previous section, a traditional asset of the MMPI/MMPI-2/MMPI-A has been extensive and ongoing code type studies.
However, difficulties with these studies have been recently noted. First, some studies have tried to be extremely inclusive in deciding which codes to evaluate. In contrast, others have been quite restrictive (i.e., including only clearly defined code types).
Inclusion/exclusion among the different studies has ranged from 24 to 99% (McGrath & Ingersoll, 1999a).
The practical implication for clinicians is considering the degree to which their code type classifications parallel those of research.
If specific clinicians are highly inclusive about what they consider to be interpretable code types, they may place unwarranted faith in their interpretations if the body of research they are drawing from has used quite restrictive criteria (i.e., J. Gr aharn et aI., 1999 used only well-defined code types).
A further concern is that the mean effect size across studies was quite variable, with a high of .74 and low of .02 (McGrath & Ingersoll, 1999b; G. Meyer & Archer, 2001).
In addition, effect sizes were found to vary among different scales and code types. Therefore, practitioners may not only be placing unwarranted faith in some of their interpretations, but also the validity of the interpretations they do make are likely to vary according to which scale/code type they are interpreting.