Childhood evacuation during World War II and subsequent cognitive ability: The Scottish Mental Survey 1947

Childhood evacuation during World War II was reported by a recent Finnish study to be associated with lower intelligence at follow-up in to early and late adulthood (Pesonen et al., 2011, 2013). Opportunities of conducting such natural experiment studies are rare, and yet they contribute to understanding impacts of the early life environment on cognitive development and ability. We investigated the association between evacuation and later cognitive ability in a different national sample. This included 6,082 pre-school boys and girls, 768 of whom were evacuated from their homes in Scotland between 1939 and 1945. The mean duration of evacuation was 14.8 months (SD = 17.8, Mdn = 7.0). Cognitive ability was measured at age 11, in 1947, using the Moray House Test (No. 12). Evacuated children scored on average 1.5 points higher on intelligence test scores relative to their non-evacuated peers (Cohen’s d = 0.10, p = .038). The p value was .070 after controlling for potential confounders, including socioeconomic status. These findings, in contrast with those from Finland, raise the possibility that evacuation in Scotland may have had a small positive effect on children’s cognitive ability scores, due to a difference in educational and environmental exposures. However, analysis of a subset of results using sibling intelligence data, could not rule out selection bias, caused by higher intellectual-ability parents’ being more likely to volunteer their children for evacuation. Nevertheless, any supposed adverse effect of evacuation on children in Scotland was not reflected in subsequent intellectual performance.