A comparison of low IQ scores from the Reynolds Intellectual Assessment Scales and the Wechsler Adult Intelligence Scale-Third Edition.

The team gave two IQ tests to adults with suspected intellectual disability. One test was the Reynolds Intellectual Assessment Scales. The other was the Wechsler Adult Intelligence Scale-Third Edition.

They wanted to see if the two tests gave the same IQ scores.

The Reynolds test gave higher IQ scores than the Wechsler test. The difference showed up in the nonverbal part, not the verbal part.

This means the same person could look more capable or less capable depending on which test you pick.

Mazur et al. (1992) showed that Wechsler scores stay stable for years in adults with ID. So big jumps or drops are probably real, not error.

Green et al. (2020) found the same kind of score shift with the Vineland adaptive tests. Vineland-3 scores run 10-20 points lower than Vineland-II for the same person.

Together these papers warn that test edition matters. Swapping tests can change eligibility for services.

If you test an adult with ID and the score is near the cutoff, pick your test on purpose. A Reynolds IQ might push the person above the line and out of services. A Wechsler IQ might keep them in. Always report which test you used and let the team decide if retesting is fair.