“‘Constancy’ of the IQ”, Robert L. Thorndike1940 (IQ; backlinks)⁠:

The author presents a critical review of the studies of the stability of intelligence-test performance by the same individual over a considerable period of time, with special reference to studies which have appeared since 1930.

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It is the purpose of this article to review recent experimental evidence on the stability of intelligence test performance by the same individual over a lapse of time. The content of the review will be limited in two ways:

1. It is proposed to consider chiefly those reports which have appeared since 1930–1931_93ya. The literature previous to that time has been covered by Nemzek (75), Foran (24, 25), and others. Earlier studies will be referred to only as this becomes necessary to understand recent trends of investigation.

2. It is proposed to limit this report primarily to those investigations in which the same individuals have been tested more than once. Although studies of the resemblance of relatives, the intelligence level of occupational groups, etc. provide evidence concerning the relative weight of hereditary, as opposed to environmental, factors in producing differences in intelligence test performance, and consequently bear on the stability of the performance of the individual, it is not our purpose to try to cover this broader literature here.

Certain general trends seem to appear in the type of experimentation reported within the last 8 years, and it might be profitable to consider these briefly before going on to a survey of findings. In the period now being studied, the general fact of a rather high positive correlation between test and retest after an interval of time in children of school age seems to be fairly well taken for granted, and relatively few studies were found which were concerned merely with demonstrating this point. Most studies try to push this finding forward in one or another of several directions, of which the following are rather typical: (1) attempts to get retest information on younger and younger children; (2) efforts to get retest data over longer periods of time; (3) efforts to determine the effect upon test constancy of particular types of environmental manipulation.

See Also:

• Constancy of IQ scores among gifted children

• The stability of educational achievement across school years is largely explained by genetic factors

• Developing talents: A longitudinal examination of intellectual ability and academic achievement

• Interindividual differences in general cognitive ability from age 18 to age 65 years are extremely stable and strongly associated with working memory capacity

• The cross-cultural generalizability of cognitive ability measures: A systematic literature review

• Everyday Life as an Intelligence Test: Effects of Intelligence and Intelligence Context

• Psychological Assessment Versus Psychological Testing: Validation From Binet to the School, Clinic, and Courtroom

• Life cycle patterns of cognitive performance over the long run

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