Even if they reject the evidence that cognitive impairment follows onset of the illness in many (but by no means all) patients with schizophrenia as reported by most investigators from Kraepelin R5515511CHDDIACA onward R5515511CHDBDDCDR5515511CHDCJBDJ, the data presented by Russell et al. fail to support their conclusion that "the deficit in intellectual function observed in these patients, and reported in the literature, is lifelong and predates the onset of schizophrenia." In contrast to the majority of adults with schizophrenia, for whom the premorbid intelligence and mental statuses are within normal limits R5515511CHDBDDCD, the mean childhood IQ score for the cohort of Russell et al. was 82.4; as children, at least 10 patients had IQs below 80, and 38% were diagnosed with psychotic disorders. Of 10 patients with IQs below 80 at the childhood examination, the IQs of only two declined, and the IQs of seven increased at follow-up. In contrast, five of six patients with initial IQs of 100 or above had a decrease in IQ of 10–20 points between the first examination and the second 20 years later. Averaging the scores from the first examination for all the patients and comparing these scores with averaged scores from the second examination 20 years later yielded an almost unchanged mean score for the entire cohort at follow-up. The authors suggest this is an example of "regression to the mean." However, a decline of IQ by 15–20 points between late childhood and adult life is not a usual occurrence and requires a nonstatistical explanation. Moreover, their regression analysis found that the time 1 IQs explained only 60% of the variance in time 2 IQs, even after they corrected for age, sex, and so forth; this finding leads to the inference that something else, perhaps schizophrenia, played a role here.