Whenever I've heard people make the comment: "....of course, it is because you (he/she) is a first (second, etc.) born in your family".......I have always cringed. Even if some of the significant findings that have been reported in individual studies are real, the correlations (and effect sizes) are typically small....too small to make blanket generalizations re: birth order being the end all explanation for someone's certain behavior, outcomes in life, etc. Yet....people like to believe in these simplistic psychological notions.
Today, a news report directed my attention to a methodologically sound large-scale study that discounts the relationship between birth order and intelligence. The abstract for the study mentioned in this news release (below), along with a link to the article (click here), are provided for readers of IQs Corner. The news report, abstract, and complete article should be of interest to those who want to present a balanced picture to the general public regarding the importance of birth order and intelligence.
- Many studies show relationships between birth order and intelligence but use cross-sectional designs or manifest other threats to internal validity. Multilevel analyses with a control variable show that when these threats are removed, two major results emerge: (a) birth order has no significant influence on children’s intelligence and (b) earlier reported birth order effects on intelligence are attributable to factors that vary between, not within, families. Analyses on 7- to 8- and 13- to 14-year-old children from the National Longitudinal Survey of Youth support these conclusions. When hierarchical data structures, age variance of children, and within-family versus between-family variance sources are taken into account, previous research is seen in a new light.
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