Monday, August 27, 2007

IQ trends



Glancing at GSS data on IQ (based on a vocabulary test) it looked to me like scores, for both blacks and whites, have been moving away from the extremes over the past 35 years. A closer look shows that I was more or less right. The bottom two graphs above are from 1973 to 2006. The top graph shows that percent with a particular score--6 is modal. To smooth the trends, I merged those with low scores (0-5); those with average scores (6-9); and those with perfect 10s. (I decided on these categories based on what appeared to move together over time). On the graphs, 3 (or green) is for the high group, 2 (or blue) for the middle, and 1 (or red) for the low group.

For both races, the low IQ group has shrunk while the middle group has grown, but this upward movement for blacks appeared only after 1994. It is not clear if the prevalence of high IQ blacks has increased, but the number for whites has dropped from 9 to 4%.


  1. Is it age related? Are folks who never got much schoolin' finally dying off?

  2. What interests me most is the decline in the high-IQ percentage of whites. It can't be a statistical fluke, the trend is unmistakeable.

    I don't believe that in 35 years there could really be such genetic change.

    Is it perhaps the effect of less reading and more TV and game-playing?

    Or perhaps the intelligent are having greater success in evading the pollers?

  3. The bug drop in verbal SAT scores occurred in the sixties and early seventies. This drop occurred even at the top. See here.


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