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 138.25 and the standard deviation was 18.86. 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
FSIQ revealed no significant difference between the two measures. The mean Estimated FSIQ was 138.19 with a standard deviation of 18.81. 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).
Contest Composite Estimated WAIS FSIQ 95% Confidence Interval 95 161 169 94 160 168 93 159 167 92 157 165 91 156 164 90 155 163 89 154 162 88 153 161 87 152 160 86 151 159 85 150 158 84 149 157 83 148 157 82 148 156 81 147 155 80 146 154 79 145 153 78 144 152 77 143 151 76 142 150 75 141 149 74 140 148 73 139 147 72 138 146 71 137 145 70 136 144 69 135 143 68 134 142 67 133 141 66 132 140 65 131 139 64 130 138 63 129 137 62 128 136 61 127 135 60 126 134 59 125 133 58 123 131 57 122 130 56 121 129 55 120 128 54 119 127 53 118 126 52 117 125 51 116 124 50 115 123 49 114 122 48 113 122 47 113 121 46 112 120
Contest Composite Estimated WAIS FSIQ 95% Confidence Interval 45 111 119 44 110 118 43 109 117 42 108 116 41 107 115 40 106 114 39 105 113 38 104 112 37 103 111 36 102 110 35 101 109 34 100 108 33 99 107 32 98 106 31 97 105 30 96 104 29 95 103 28 94 102 27 93 101 26 92 100 25 91 99 24 90 98 23 88 96 22 87 95 21 86 94 20 85 93 19 84 92 18 83 91 17 82 90 16 81 89 15 80 88
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), 499-506. Wechsler, D. (1997). Wechsler Adult Intelligence Scale (3rd ed.). New York: The Psychological Corporation.