One of the most fascinating case studies in the anals of WAIS history was a 17-year-old male known only as D-2 who was tested sometime in the 1950s, presumably at the legendary Bellevue psychiatric hospital where the great David Wechsler himself worked as chief psychologist from 1932 to 1967. So legendary is the Bellevue mental hospital, that Bellevue has entered the culture as slang for “nut house”.

D-2 scored in the “mentally defective” range which Wechsler defined as below IQ 70 (bottom 2% of America) .

Wechsler wrote of this patient:

Patient’s present admission followed a long history of aberrant behavior. At age of 8 committed by court to institution for mental defectives because of antisocial behavior. At that time considered by the court to be a “psychopath”. Discharged after about two years, but soon recommitted for stealing. Mother of dull-normal intelligence; likewise father. who had frequent incarcerations in penal institutions for various crimes, and had been diagnosed as paranoid schizophrenic.

Since average range intelligence is considered 90 to 109 (the middle 50% score in this range), the term dull-normal described those with IQs in the 80s. Here we see an example of how regression works both ways. Just as the children of mentally impaired parents (IQ < 70) tend to score high than their parents, but not as high as the average American; the parents of mentally impaired children tends to score higher than their children, but also below 100.

Wechsler continues:

Reported psychometric, is a re-test given on admission to present institution. On examination patient reported to be very distractible and showing generally poor attention. Impression of examiner was that one was dealing with a psychotic rather than a defective individual, and same was confirmed by projective tests. Patient was preoccupied with sexual fantasies, many of a primitive sort. During the examination he asked examiner if she would have sexual intercourse with him.

Wechsler then goes on to explain that D-2’s WAIS profile was far more variable than that of the typical “defective”:

His scores range from 0 on Digit Symbol to 9 on Digit Span. He was hardly able to get started on the Digit Symbol Test; his attention wandered. He was at once confused and frustrated by the task. At first approach, one might suspect that the over-all low performance might be ascribed to the psychotic process but while this undoubtedly served to interfere with his “efficiency,” the systematic poor performance on Vocabulary and Similarities, as well as the Block Design, support the view that in addition to any mental disturbances we are dealing with an individual of basically limited mental endowment. Diagnosis of psychosis with mental deficiency would seem accurately to sum up his mental status. Whether this patient might not do better in a state mental hospital rather than an institution for mental defectives needs to be considered. In this connection it should be noted, however, that a substantial percentage of patients in feeble-minded domiciliaries are undoubtedly also psychotic.

Once again we see how essential the Digit Symbol subtest is at detecting deficiencies other subtests miss.

Below are D-2’s WAIS scores. Note that the IQs (stated in bold) are set to have a U.S. mean of 100 and a standard deviation of 15. The subtest scores are expressed using a scale with a mean of 10 and a SD of 3. This is somewhat analogous to the distribution of adult male height in Western countries, where the mean is 10 inches above five feet and the SD (typical difference from the mean) is 3 inches. Subtest scores can be converted to IQ equivalents by multiplying by 5 and then adding 50.