Psychologists are split on the existence of “birth order effects”, where oldest siblings will have different personality traits and outcomes than middle or youngest siblings. Although some studies detect effects, they tend to be weak and inconsistent.

Last year, I posted Birth Order Effects Exist And Are Very Strong, finding a robust 70-30 imbalance in favor of older siblings among SSC readers. I speculated that taking a pre-selected population and counting the firstborn-to-laterborn