I suspect the findings in this article might be correlated with the reduction in lead exposure over the same timeframe. I wonder if the greater reduction in early-childhood blood lead for blacks might be sufficient to explain the effect described in the study.
Richard B. Mott Ringoes, N.J.
What can we conclude from these facts? Not much, because, as the psychometrician states, we do not actually know what intelligence is, nor do we know what intelligence tests actually measure other than performance on the tests themselves.
David P. Vernon Tucson, Ariz.
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