SQ variability of +/- 7 points is considered OK for IQ tests. Both SQ and IQ scores center around 100 and show similar standard distributions of scores. The quotes below from a major IQ test firm indicate that a reliability of +/- 7 points is "larger" than normal for IQ, but within the acceptable range.

The Wechsler Adult Intelligence Scale (WAIS) is "the most widely used and researched intelligence scale for adults" according to its publisher, The Psychological Corporation, a division of Harcourt Brace & Company. (It's only major rival in IQ tests is the Stanford-Binet, published by a division of by Houghton Mifflin.)

Two senior project directors of The Psychological Corporation conducted a study in 1999 on IQ measurement error in administering their WAIS-III and their WASI, an abbreviated IQ test. Their study included three samples of non-clinical adolescents and adults aged 16-89 who participated in the 1996 WASI validity study. Results for samples 1 and 2 (totaling 298 individuals) "revealed only small discrepancies...within +2 -2.5 for IQ and index scores."

Results for sample 3 (of 124 cases) showed a "larger" variation: "90 to 98 percent of the discrepancies between the observed and estimated scores are within the range of 5 to 7 points." Nevertheless the corporation writes: "Overall, clinicians can be assured that either method of administration will provide accurate and efficient assessments."

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