Dr. Alan Kaufman has summarized the majority of the literature on practice effects on the Wechslers. He published an article in The Encyclopedia of Intelligence (1994; Edited by Robert Sternberg) that summarized the research prior to the third editions of the Wechsler scales. That article is available on-line (click here).
The most recent summary of the contemporary Wechsler practice effect research is in Lichtenberger and Kaufman (2009) Essentials of WAIS-IV Assessment (p. 306-309). The tables and text provide much about WAIS-IV and some about WAIS-III. The best source for WAIS-III is Kaufman and Lichtenberger, Assessing Adolescent and Adult Intelligence (either the 2002 second edition or the 2006 third edition), especially Tables 6.5 and 6.6 (2006 edition). Below are a few excerpts from the associated text from the 2006 edition
"Practice effects on Wechsler's scales tend to be profound, particularly on the Performance Scale" (p. 202)
"predictable retest gains in IQs" (p.202)
"On the WAIS-III, tests with largest gains are Picture Completion, Object Assembly, and Picture Arrangement"
"Tests with smallest gains are Matrix Reasoning (most novel Gf test), Vocabulary and Comprehension
Block Design improvement most likely due to speed variance--"on second exposure subjects may be able to respond more quickly, thereby gaining in their scores" (p. 204)
One year interval results in far less pronounced practice effects (p. 208).
"The impact of retesting on test performance, whether using the WAIS-III, WAIS-R, other Wechsler scales, or similar tests, needs to be internalized by researchers and clinicians alike. Researchers should be aware of the routine and expected gains of about 2 1/2 points in V-IQ for all ages between 16 and 89 years. They should also internalize the relatively large gain on P-IQ for ages 16-54 (about 8 to 8 1/2 points), andn the fact that this gain in P-IQ swindles in size to less than 6 points for ages 55-74 and less than 4 points for ages 75-889" (p. 209).
"Increases in Performance IQ will typically be about twice as large as increases in Verbal IQ for individuals ages 16 to 54" (p. 209)
Finally, the latest AAIDD manual provides professional guidance on the practice effect.
"The practice effect refers to gains in IQ scores on test of intelligence that result from a person being retested on the same instrument" (p. 38)
"..established clinical practice is to avoid administering the same intelligence test within the same year to the same individual because it will often lead to an overestimate of the examinee's true intelligence" (p. 38).
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On January 7, Colorado Governor Bill Ritter granted a full and unconditional posthumous pardon to Joe Arridy, who had been convicted and executed as an accomplice to a murder that occurred in 1936. The pardon came 72 years after Arridy's execution and is the first such pardon in Colorado history. A press release from the governor's office stated, "[A]n overwhelming body of evidence indicates the 23-year-old Arridy was innocent, including false and coerced confessions, the likelihood that Arridy was not in Pueblo at the time of the killing, and an admission of guilt by someone else." The governor also pointed to Arridy's intellectual disabilities. He had an IQ of 46 and functioned like a toddler. The governor said, "Granting a posthumous pardon is an extraordinary remedy. But the tragic conviction of Mr. Arridy and his subsequent execution on Jan. 6, 1939, merit such relief based on the great likelihood that Mr. Arridy was, in fact, innocent of the crime for which he was executed, and his severe mental disability at the time of his trial and execution. Pardoning Mr. Arridy cannot undo this tragic event in Colorado history. It is in the interests of justice and simple decency, however, to restore his good name."
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