USE OF THE TELLEGEN AND Briggs formula TO DETERMINE the

USE OF THE TELLEGEN AND Briggs formula TO DETERMINE the Canadian Dumont-Willis-Beal Indexes (CAN-DWBI-1 & CAN-DWBI-2) for the Canadian WISC-IV[1]

Ron Dumont, John O Willis and A. Lynne Beal

In this short paper, we provide two alternative composite scores (CAN-DWBI-1 and CAN-DWBI-2) for the WISC-IV with Canadian norms. CAN-DWBI-1 is derived from the three subtests that enter the VCI and the three subtests that enter the PRI. CAN-DWBI-2 is derived from the two subtests that enter the WMI and the two subtests that enter the PSI. We refer to these composites as the Canadian Dumont-Willis-Beal Indexes (CAN-DWBI’s) in order to distinguish them from the traditional ten-subtest Full Scale IQ. The Canadian Dumont-Willis-Beal Indexes separates the six subtests that are stronger measures of verbal and non-verbal intelligence from the other four subtests that are not as highly correlated with FSIQ (i.e., Digit Span, Letter-Number Sequencing, Coding, and Symbol Search).

The CAN-DWBI-1 score is a six-subtest composite that excludes subtests which load on the WMI and PSI.

The CAN-DWBI-2 score is a four-subtest composite that includes subtests which load on the WMI and PSI.

Examiners may wish to report CAN-DWBI’s when the Verbal (VCI) and Perceptual (PRI) abilities are found to be close to one another yet significantly different from those of the Working Memory (WMI) or Processing Speed (PSI) abilities.

The tables for the CAN-DWBI’s are provided below. These tables were developed using the procedures described for the American Dumont Willis Index 1 (DWI-1) and the Dumont-Willis Index-2 (DWI-2). The procedure uses the WISC-IV Canadian subtest intercorrelations (Table 5.1, page 67, WISC-IV Canadian Manual[2]) and the Tellegen and Briggs procedure[3]. Conceptually, the Canadian Dumont-Willis-Beal Index-1 parallels the General Ability Index (GAI) developed by Prifitera, Weiss, and Saklofske[4] for the sum of scaled scores for the eight VCI and POI subtests of the WISC-III. Prifitera, Weiss, and Saklofske's table was based directly on the WISC-III Canadian normative data.

Similarly, the Canadian Dumont-Willis-Beal Index-2 is based on the sum of scaled scores for the Digit Span and Letter-Number Sequencing (WMI) and Coding and Symbol Search (PSI) subtests. This score is very similar to Alan Kaufman's "third factor"[5] and "SCAD"[6] scores. It should be computed and considered only when the four WMI and PSI subtest scores are close to one another and substantially separate from the VCI and PRI subtests. In those cases, the CAN-DWBI-1 and CAN-DWBI-2 scores may be an efficient alternative means of summarizing the 10 WISC-IV core subtests, but they must never be confused with Canadian normative WISC-IV factor and IQ scores.

To use these tables, first calculate the Canadian Dumont-Willis-Beal Index-1 Sum of Scaled Scores (CAN-DWBI-1 SSS) by adding the scaled scores for the following six subtests: Similarities, Vocabulary, Comprehension, Block Design, Picture Concepts, and Matrix Reasoning.

Second, calculate the Canadian Dumont-Willis-Beal Index-2 Sum of Scaled Scores (CAN-DWBI-2 SSS) by adding the scaled scores for the following four subtests: Digit Span, Letter-Number Sequencing, Coding, and Symbol Search.

Using the appropriate table (CAN-DWBI-1 or CAN-DWBI-2), find the resulting Canadian Dumont-Willis-Beal Index Sum of Scaled Scores in the column labeled "Sum of CAN-DWBI SSS" in the Tables below and read across the row to determine the CAN-DWBI score, associated percentile rank, and 95% confidence interval (based upon the Standard Error of Estimate). Be sure to use the "CAN-DWBI-1: VCI + PRI" table for the six Verbal Comprehension and Perceptual Reasoning subtests (you will see that a SSS of 60 equals a standard score of 100). Use the "CAN-DWBI-2: WMI + PSI" table for the four Working Memory and Processing Speed subtests (you will see that a SSS of 40 equals a standard score of 100).

Estimates of overall abilities calculated in this way should always be clearly identified as CAN-DWBI scores in both text and tables of reports. These scores must not be confused with the Full Scale IQ, although they may be more useful estimates of intellectual ability in some cases, for example, for some gifted children and for some children with relative weaknesses in Working Memory and/or Processing Speed. For the latter group, the CAN-DWBI’s may help avoid Dumont and Willis's Mark Penalty,[7] the depression of a measure of intelligence by a low score on a measure of a student's specific weakness. Other children may score significantly higher on the WMI and PSI indices than on the VCI and PSI indices, which may mask important difficulties with conceptual thinking if the FSIQ is used without the CAN-DWBI’s.

The equivalent tables for the U.S. WISC-IV and additional information about the Tellegen and Briggs formulas are posted at http://alpha.fdu.edu/psychology.