Examiner effects in adoption studies of intelligence.

To test the hypothesis that examiner differences influence family correlations in adoption studies of intelligence, data from two recent adoption studies were reanalyzed as a function of whether the same or different examiners tested both members of a pair. While each study yielded trends suggesting examiner effects on correlations, results of the two studies were directly counter to each other. Our conclusion is that examiner effects are not yet predictable and, overall, cannot be demonstrated to bias adoption studies of intelligence.