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The influence of chronological age and family environment on the performance in crystallized intelligence markers was studied in a group of persons with mental retardation aged from 6 to 20 years. Twelve fluid and crystallized intelligence markers were administered. In order to identify underlying factors, principal components and common factors analyses were carried out. Because the tests were mainly fluid and crystallized ones, it was not surprising that the application of the Kaiser- Guttman criterion clearly indicated two factors to be extracted from the correlation matrix among raw scores. The first factor had high loadings on crystallized intelligence tests, whereas the second loaded principally fluid ones. Fluid intelligence level of each participant was then determined using the mean z scores in fluid markers, and stepwise regression analyses were performed to estimate the relative contribution of CA and family environment to the crystallized intelligence tests' variance. In these analyses, fluid intelligence level was systematically entered first in the equations to partial out at the outset its influence from those of CA and family environment. Results indicate that chronological age explains an important fraction of the crystallized intelligence markers variance (from 5 to 24 % ), whereas the family environment influence appears much more modest (from 0 to 3 %). However, this result seems to be attributable to the characteristics of the family environment scale used in the present study and to the restricted range of family environments in the sample.
