Effects of age and schooling on intellectual performance: Estimates obtained from analysis of continuous variation in age and length of schooling

The effects of age and schooling on different aspects of intellectual performance, taking track of study into account, are investigated. The analyses were based on military enlistment test scores, obtained by 48,269 males, measuring Fluid ability (Gf), Crystallized intelligence (Gc), and General visualization (Gv) ability. A regression method, relying on simultaneous variation in age and length of schooling at the time of the testing, was used. The results showed that both age and schooling increase performance, with the exception of the test which primarily measures Gf, for which the age effect was negative. The effects of schooling were considerably stronger than the effects of age, and there was a pattern of differential schooling effects on different tests which matched the curricular emphasis of the programs. The estimates of the strength of the schooling effect obtained with this new method were generally in good agreement with the results obtained in previous research.