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WPPSI III® SUBSTITUTION

The WPPSI III® allows examiners the option of substituting certain “supplemental” subtests for other “Core” subtests. [The WPPSI III® Manual (pg 25) notes that a total of only two substitutions can be made for any of the 7 core subtests if one wishes to obtain a Full Scale IQ.]  For the Verbal I, either the Comprehension or the Similarities subtest can substitute for one of the core verbal subtests (only 1 substitution allowed per administration).  For the Performance IQ, either the Picture Completion or the Object Assembly can substitute for one of the core subtests (again, only 1 substitution per administration). For the computation of a FSIQ, either Coding or Symbol Search may be used. These substitution rules results in 7 possible Verbal IQ configurations and 7 Performance IQ configurations.  Since the 7 Verbal IQ combinations can combine with any one of the 7 Performance IQ combinations, the results is a total of 49 possible test combinations for just the Verbal and Performance IQs.  Add to this the opportunity to use either the Coding (core) or Symbol Search (supplemental) subtests, there are a total of 63 seven-subtest combinations available when computing the Full Scale IQ of the WPPSI III®.  Table 1 presents the 7 Verbal IQ and 7 Performance IQ combinations.

Since only 2 substitutions are allowed in any 7 subtest combination that results in a FSIQ, all the possible combinations are:

Forty-Nine Combinations that include one Verbal and one Performance substitution along with the Coding (core) subtest.

If Symbol Search is used as a substitution for Coding, it limits the second substitution to either the Verbal scale (seven combinations) or the Performance scales (seven combinations):

Verbal Subtests’ Correlations

Table 2 below provides the correlation between the core Verbal subtests and the supplemental subtests as well as the two General Language subtests.  While the three core subtests correlate very well with the VIQ (range .89 to .91) the two supplemental tests both had lower correlations (.75 and .76).  The three core subtests also correlated better with the FS IQ (range .78 to .82) than did the two supplemental subtests (.71 and .73).  Comprehension correlated best with Vocabulary and Word Reasoning while Similarities has approximately equal correlations with the core subtests.   Oddly, the two general language subtests correlated better with Information and Word Reasoning (.65 to .73) than with Vocabulary (.59 and .63)

Performance Subtests’ Correlations

Table 3 below provides the correlations between the core Performance subtests and the supplemental subtests.  While the three core subtests correlate with the PIQ very well (range .79 to .82), the two supplemental tests both had lower correlations (.59 and .70).  The three core subtests also correlated better to the FS IQ (range .71 to .74) than did the two supplemental subtests (.66 and .55).  Picture Completion and Object Assembly both correlated best with Block Design (.50 and .53).

Processing Speed Subtests’ Correlations

Both the Coding and Symbol Search subtests correlate equally with the PS Quotient (.89), while SS correlates slightly better to the FS than does Cd.

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