Secular trends in cognitive test performance: Swedish conscript data 1970–1993

We investigated time-related patterns in levels of cognitive performance during the period from 1970 to 1993 based on data from Swedish draft boards. The conscripts, including more than a million 18–19-year old men, had taken one of two versions of the Swedish enlistment battery (SEB67; 1970–1979 or SEB80; 1980–1993), each composed of four subtests. The results revealed significant Flynn effects, with estimated gains of 1.2–1.5 IQ-units per decade. The effect seem to hold across ability levels, even though tendencies of more pronounced effects in the lower half of the ability distribution was observed. The largest gains were for visuospatial tests (Paper Form Board and Metal Folding), with little change, even slight losses during the second sub-period, for tests of verbal knowledge (Concept Discrimination and Synonyms) and a mixed pattern for a test of technical comprehension (losses followed by gains). Finally, comparisons of trends in cognitive performance and in standing height show that the gains in cognitive performance over the years from 1980 to 1993 occurred in the absence of overall gains in height, which speaks against nutrition as the cause of the Flynn effects.