[Uncertainty on the measurement of intelligence].

In recent years, there has been considerable evidence on the phenomenon of intelligence quotient (IQ) gains over time with a gain rate of approximately three IQ points per decade. This phenomenon has been called the Flynn effect. This review article presents the evidence that supports this effect and discusses its implications for the measurement of intelligence. The above mentioned IQ gains over time obviously present serious methodological and theoretical problems in the use of intelligence tests. We review the methodological consequences which the Flynn effect presents in the reliability of the measurement of IQ as well as the methodological consequences which this effect has for epidemiological studies, especially those which focus on the study of the prevalence of mental retardation. Mention is made of the hypothesis that tries to explain these IQ gains, analyzing those which tend to explain these IQ gains as real gains in intelligence, as well as those that propose that these gains are due to other causes rather to real population IQ gains.