This is a follow-up to my brief comments yesterday regarding the Johstone v Fl (2010) denied MR/ID appeal of two days ago.
As mentioned in the decision and my blog comment, the WAIS-III/WAIS-IV tests correlated .94 in a study reported in the WAIS-IV technical manual. This is a very high correlation...but does NOT mean that the two tests should be expected to provide identical IQ scores. I discuss these issues in a prior IAP AP101 report.
The tests have different norm dates and thus, the later version (WAIS-IV) would be expected to provide a lower score based on the Flynn effect. More importantly, as reported in the IAP AP101 report, when one calculates the standard deviation of the difference score (see page 6 of that report) for a correlation of .94, the resulting value is 5.2 (round to 5 for ease of discussion). This means that, on average, the WAIS-III/WAIS-IV (even if highly correlated at the .94 level) would in the general population be expected to display a range of difference scores from -5 to +5...or a range of 10 IQ points......in 68% of the population. Please review that prior report for further explanation and discussion.
Technorati Tags: psychology, forensic psychology, forensic psychiatry, neuropsychology, intelligence, school psychology, psychometrics, educational psychology, IQ, IQ tests, IQ scores, intellectual disability, mental retardation, MR, ID, criminal psychology, criminal defense, criminal justice, ABA, American Bar Association, Atkins cases, death penalty, capital punishment, AAIDD, scientific evidence, Flynn effect, validity, norms, practice effects, Johnstone v Florida, WAIS-III, WAIS-IV, CHC intelligence theory, CHC, Cattell-Horn-Carroll, Daubert standard
As mentioned in the decision and my blog comment, the WAIS-III/WAIS-IV tests correlated .94 in a study reported in the WAIS-IV technical manual. This is a very high correlation...but does NOT mean that the two tests should be expected to provide identical IQ scores. I discuss these issues in a prior IAP AP101 report.
The tests have different norm dates and thus, the later version (WAIS-IV) would be expected to provide a lower score based on the Flynn effect. More importantly, as reported in the IAP AP101 report, when one calculates the standard deviation of the difference score (see page 6 of that report) for a correlation of .94, the resulting value is 5.2 (round to 5 for ease of discussion). This means that, on average, the WAIS-III/WAIS-IV (even if highly correlated at the .94 level) would in the general population be expected to display a range of difference scores from -5 to +5...or a range of 10 IQ points......in 68% of the population. Please review that prior report for further explanation and discussion.
Technorati Tags: psychology, forensic psychology, forensic psychiatry, neuropsychology, intelligence, school psychology, psychometrics, educational psychology, IQ, IQ tests, IQ scores, intellectual disability, mental retardation, MR, ID, criminal psychology, criminal defense, criminal justice, ABA, American Bar Association, Atkins cases, death penalty, capital punishment, AAIDD, scientific evidence, Flynn effect, validity, norms, practice effects, Johnstone v Florida, WAIS-III, WAIS-IV, CHC intelligence theory, CHC, Cattell-Horn-Carroll, Daubert standard
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