Sibling resemblance in mental ability: A review

Abstract

Empirical evidence on sibling resemblance in intelligence published since 1915 in the United States and Europe, including more than 27,000 sibling pairs, is reviewed. The results of these investigations are presented in tables showing the date, investigator, test, sample size, and correlations found for each specific study. Collectively, the results are highly consistent with the polygenic hypothesis and the conclusion that genetic factors are the major source of individual differences in intelligence. The most likely estimate of the sibling correlation for IQ in the population is +0.49.

Relationship between the IQ of people with Prader–Willi syndrome and that of their siblings: evidence for imprinted gene effects

“…In the former case we would expect that the correlation between PWS IQ and sibling IQ would be similar to that found in the general population, i.e. 0.5 (Paul 1980). In the latter case, we would expect the correlation to be near zero, i.e.…”

Vulnerability to insomnia: The role of familial aggregation

“…FIRST scores were converted to z-scores and outliers were considered to be present if a score deviated by ±2. As documented in previous sibling studies [16], the most appropriate method for assessing the relationship between sibling pairs on a given variable when there is no reason for assigning one member of a pair to a particular group (X's) and the second to another (Y's) is the intraclass correlation coefficient (ICC). Thus, the ICC was utilized in the present study to determine the correlation between sibling pairs on the FIRST scale.…”

Cognition in people with Prader-Willi syndrome: Insights into genetic influences on cognitive and social development

“…A further difference was found between people with the two main genetic sub-types when the correlations between PWS and sibling IQs were investigated (Whittington et al 2009). The usual correlation (Paul 1980) of 0.5 between sibling pairs was found between those with PWS due to UPD (n=10) and their siblings but the correlation between those with PWS due to a deletion (n=18) and their siblings was zero. The correlation between all non-PWS sibling pairs in this study was the expected 0.5.…”