Huh - all that talk and research for years about the first born being the smartest and most responsible. Yes...but according to this large study comparing 377,00 high school students from different families, the differences are so small as to be meaningless (1 IQ point!). Researchers looking within-families (studying siblings within families) say that the effects are larger. Depends on who you want to believe. And this study did not look at the siblings later in life - at achievements, etc. From Medical Xpress:
For those who believe that birth order influences traits like personality and intelligence, a study of 377,000 high school students offers some good news: Yes, the study found, first-borns do have higher IQs and consistently different personality traits than those born later in the family chronology. However, researchers say, the differences between first-borns and "later-borns" are so small that they have no practical relevance to people's lives. The analysis found - as a previous large-scale study did - that first-borns enjoy a one-IQ-point advantage over later-borns, Damian said. The difference is statistically significant but meaningless, she said.
The analysis also revealed consistent differences in personality traits between first-borns and later-borns - first-borns tended to be more extroverted, agreeable and conscientious, and had less anxiety than later-borns, for example - but those differences were "infinitesimally small," amounting to a correlation of 0.02, Roberts said. "But in terms of personality traits and how you rate them, a 0.02 correlation doesn't get you anything of note. You are not going to be able to see it with the naked eye. You're not going to be able to sit two people down next to each other and see the differences between them.."
The study controlled for potentially confounding factors - such as a family's economic status, the number of children and the relative age of the siblings at the time of the analysis - that might skew the results, Damian said. For example, wealthier families tend to have fewer children than other families, and so have a higher proportion of first-borns who also have access to more resources that may influence their IQ or personality, she said.
Many previous studies of birth order suffered from small sample sizes, Damian said. Many compared children with their siblings - a "within-family" design that some assert is better than comparing children from different families, as the new analysis did.
The team also evaluated a subset of the children in the study - those with exactly two siblings and living with two parents. This allowed the researchers to look for specific differences between first- and second-borns, or second- and third-borns. The findings confirmed those seen in the larger study, with specific differences between the oldest and a second child, and between second and third children. But the magnitude of the differences was, again, "minuscule," Roberts said.