First children have higher IQs than their siblings

A paper published in 2015 by researchers from the University of Leipzig in Germany and elsewhere, titled “Examining the effects of birth order on personality,” is a research report that investigated differences in intelligence and personality based on birth order. The study looked at data from a total of approximately 20,000 people from the United States, the United Kingdom, and Germany, and conducted a detailed analysis of differences based on birth order in IQ as well as major personality traits (extraversion, emotional stability, agreeableness, conscientiousness, and openness). The analysis was limited to families with four or fewer siblings and excluded twins. This is because twins are a special case and normal birth order effects may be different. Additionally, families with five or more siblings were excluded because they made up less than 11% of the total sample and therefore make reliable analysis difficult. The results of the analysis confirmed that, as in previous studies, intelligence tends to decline the later the birth order. The difference is about one-tenth of a standard deviation. Furthermore, there was a tendency for self-assessment of “intellectual ability” to decrease the later the birth order. This trend remained even when actual intelligence test results were taken into account. However, no significant differences were found in other personality traits based on birth order. Similar results were obtained when the analysis was restricted to cases where the age difference between siblings was 1.5 to 5 years. Read more on itmedianews 2024/11/18.

https://news.yahoo.co.jp/articles/065e90a0ae93d03c69e1bbb96c06a1495e465a05