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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Birth order | 2/3 | https://en.wikipedia.org/wiki/Birth_order | reference | science, encyclopedia | 2026-05-05T15:31:34.215227+00:00 | kb-cron |
Claims about birth order effects on personality have received much attention in scientific research, with the National Academy of Sciences in the U.S. concluding that effects are zero or near zero. Such research is a challenge because of the difficulty of controlling all the variables that are statistically related to birth order. Family size, and a number of social and demographic variables, are associated with birth order and serve as potential confounds. For example, large families are generally lower in socioeconomic status than small families. Hence, third-born children are not only third in birth order, but they are also more likely to come from larger, poorer families than firstborn children. If third-born children have a particular trait, it may be due to birth order, or it may be due to family size, or to any number of other variables. Consequently, there are many published studies on birth order that are confounded. Literature reviews that have examined many studies and attempted to control for confounding variables tend to find minimal effects for birth order. Ernst and Angst reviewed all of the research published between 1946 and 1980. They also did their own study on a representative sample of 6,315 young men from Switzerland. They found no substantial effects of birth order and concluded that birth order research was a "waste of time." More recent research analyzed data from a national sample of 9,664 subjects on the Big Five personality traits of extraversion, neuroticism, agreeableness, conscientiousness, and openness to experience. Contrary to Sulloway's predictions, they found no significant correlation between birth order and self-reported personality. There was, however, some tendency for people to perceive birth order effects when they were aware of the birth order of an individual. Smaller studies have partially supported Sulloway's claims. Paulhus and colleagues reported that firstborns scored higher on conservatism, conscientiousness and achievement orientation, and laterborns higher on rebelliousness, openness, and agreeableness. The authors argued that the effect emerges most clearly from studies within families. Results are weak at best, when individuals from different families are compared. The reason is that genetic effects are stronger than birth order effects. Recent studies also support the claim that only children are not markedly different from their peers with siblings. Scientists have found that they share many characteristics with firstborn children including being conscientious as well as parent-oriented. In her review of the research, Judith Rich Harris suggests that birth order effects may exist within the context of the family of origin, but that they are not enduring aspects of personality. When people are with their parents and siblings, firstborns behave differently from laterborns, even during adulthood. However, most people don't spend their adult lives in their childhood home. Harris provides evidence that the patterns of behavior acquired in the childhood home don't affect the way people behave outside the home, even during childhood. Harris concludes that birth order effects keep turning up because people keep looking for them, and keep analyzing and reanalyzing their data until they find them.
== Intelligence ==
In a metanalysis, Polit and Falbo (1988) found that firstborns, only children, and children with one sibling all score higher on tests of verbal ability than laterborns and children with multiple siblings. Robert Zajonc argued for a "confluence" model in which the lack of siblings experienced by firstborns exposes them to the more intellectual adult family environment. This predicts similar increases in IQ for siblings who next-oldest sibling is at least five years senior. These children are considered to be "functional firstborns". The theory further predicts that firstborns will be more intelligent than only children, because the latter will not benefit from the "tutor effect" (i.e., teaching younger siblings). Several studies have found that firstborns have slightly higher IQ than laterborns. Such data is, however, commonly confounded with family size, which is in turn correlated with IQ confounds, such as social status. Likewise, an analysis of data from the National Child Development Study has been used in support of an alternate admixture hypothesis, which asserts that the apparent birth order effect on intelligence is wholly an artifact of family size, i.e., an instance of selection pressure acing against intelligence under modern conditions. The claim that firstborns have higher IQ scores to begin with has, however, also been disputed outright. Data from the National Longitudinal Survey of Youth show no relationship between birth order and intelligence.