WAIS vs WISC vs WPPSI

Three tests, one family

David Wechsler introduced the deviation IQ with the Wechsler-Bellevue scale in 1939 (Wikipedia: WAIS). Today his name covers three separate tests for three age groups. They are revised on their own schedules, so the current editions carry different numbers: the WAIS-5, the WISC-V and the WPPSI-IV.

Sources for the table: Pearson's product pages for the WPPSI-IV (Pearson: WPPSI-IV), the WISC-V (Pearson: WISC-V) and the WAIS-5 (Pearson: WAIS-5). For the WAIS-5, about 45 minutes covers the seven Full Scale IQ subtests and about 60 minutes the ten primary index subtests.

Where the ages overlap

The ranges overlap at both joins. Children from 6:0 to 7:7 fall in both the WPPSI-IV and the WISC-V ranges, and 16-year-olds fall in both the WISC-V and the WAIS-5 ranges. In those windows the examiner picks the test that fits the person and the question the assessment is meant to answer. A 16-year-old could be assessed on either the WISC-V or the WAIS-5, and both report on the same scale.

How the index scores line up

The WISC-V and the WAIS-5 now share the same five primary indexes: Verbal Comprehension, Visual Spatial, Fluid Reasoning, Working Memory and Processing Speed (Pearson: WISC-V) (Pearson: WAIS-5 overview). Both build the Full Scale IQ from seven subtests. The older WAIS-IV used four areas instead, combining visual and fluid problems under perceptual reasoning (Pearson: WAIS-IV). The WPPSI-IV also reports a Full Scale IQ, primary index scores and ancillary index scores (Pearson: WPPSI-IV).

One scale across all three

Wechsler tests report deviation IQ scores: each age group's average is set to 100 with a standard deviation of 15 (Wikipedia: Intelligence quotient). On the WISC-V, for example, the index scores and Full Scale IQ use that scale, and 90 to 109 is typically considered average (Pearson: WISC-V UK sample report). So a WISC-V 115 and a WAIS-5 115 both mean about one standard deviation above the average for the person's age, higher than about 84% of same-age peers.

Same scale does not mean same result over time. In 225 clinic children retested on the WISC-V after an average of 2.6 years, only the Full Scale IQ, Verbal Comprehension and Visual Spatial scores had stability coefficients above 0.80 (Watkins et al., 2022). And in adults retested on the WAIS-IV after 3 or 6 months, Full Scale IQ rose about 7 points from practice alone (Estevis et al., 2012).

Which page to read next

Each test has its own page: the WPPSI-IV, the WISC-V and the WAIS-5. If you want to see what a 100-centered score means at different points on the curve, the IQ score chart lists every score from 55 to 160, and IQ classification explains the labels.

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