Estimate a WAIS Full Scale IQ with a score on the International Contest 2009

Transcription

1 Estimate a WAIS Full Scale IQ with a score on the International Contest 2009 Xavier Jouve The Cerebrals Society CognIQBlog Although the 2009 Edition of the Cerebrals Society Contest was not intended to be a measure of intelligence quotient, the reasonably close relationships observed between the three different raw scores of the questionnaire used for the contest and the self-reported Wechsler Adult Intelligence Scale, the so-called WAIS (Wechsler, 1997), allow for establishing a rough estimation table to convert Contest full scale raw scores to WAIS Full Scale IQ (FSIQ). Among the 243 contestants, 17 have reported previous WAIS FSIQ. The FSIQ above the standardization ceiling of the WAIS were extrapolated using the subtest inter-correlations of the WAIS, and the formula 4 of Tellegen and Briggs (1967). The results were increasingly underestimated over 139 FSIQ. A linear regression formula was applied in order to compensate the difference observed between estimated FSIQ and actual FSIQ. This produces a better fit of estimated FSIQ on known, standardized values. Furthermore, this method yields to extrapolated-fsiq pretty much equivalently to the Sattler s method (1992). All correlations between Contest raw scores and WAIS FSIQ exceeded.77 ; the Which Word? (WW) raw FSIQ was the lowest at.77. The Contest Composite raw score and What s Next? (WN) raw score correlated at.86 and.84 respectively with the WAIS FSIQ. In an attempt to improve the WW correlation with the WAIS FSIQ, an alternative scoring method was developed for a better adaptability relatively to the changes in crystallized-intelligence over years. On one hand, for every contestant of ages 16, 17, 18 to 19, and 20 to 29; 5, 4, 3 and 2 points were respectively added to the WW score. On the other hand, persons in ages 40 to 49 and 50 to 59 had their score respectively reduced by 3 and 4 as a result of a correlation between WW and WAIS FSIQ increased to.83. Additionally, the modified Contest Composite demonstrated a slightly better predictive validity. The correlation between new composites and WAIS FSIQ was.87. The mean FSIQ was and the standard deviation was This observation indicates that the sample covered a wide range of cognitive functioning levels, significantly larger than that of a general population representative sample. Furthermore, the mean performance showed a level that was considerably higher than that of the general population average. Even though the relative small size and the singularity of the sample, these correlations are seen as high. The estimated correspondence was derived from the Z-score equating of Contest Composites to WAIS FSIQ using the observed mean and SD of both measures. Comparison with the original WAIS

2 FSIQ revealed no significant difference between the two measures. The mean Estimated FSIQ was with a standard deviation of The correlation was.88, which indicates that the Contest Estimated FSIQ and the WAIS FSIQ had 77.4% shared and 22.6% unshared variance. Results given in the table below are presented in terms of 95 percent confidence intervals calculated with the reliability coefficient of the Contest questionnaire. The value of this coefficient as shown by the Spearman-Brown corrected split-half is.97 (N=243), which is on a comparable level than that of the WAIS battery. To be considered of a satisfactory level of reliability, a test aimed at being used for individual diagnosis should yield scores with coefficients of about.80 or higher in magnitude. Coefficients of.90 or above are considered to be most appropriate (Aiken, 2000 ; Nunnally & Bernstein, 1994).

3 Contest Composite Estimated WAIS FSIQ 95% Confidence Interval

4 Contest Composite Estimated WAIS FSIQ 95% Confidence Interval

5 References Aiken, L. R. (2000). Psychological testing and assessment (10th ed.). Needham Heights, MA: Allyn & Bacon. Nunnally, J. C., & Bernstein, I. H. (1994). Psychometric theory (3rd ed.). New York: McGraw-Hill. Sattler, J. M. (1992). Assessment of children (Rev. and updated 3rd ed.). San Diego: Jerome M. Sattler Publisher, Inc. Tellegen, A., & Briggs, P. F. (1967). Old wine in new skins: Grouping Wechsler subtests into new scales. Journal of Consulting Psychology (31), Wechsler, D. (1997). Wechsler Adult Intelligence Scale (3rd ed.). New York: The Psychological Corporation.