This hypothesis could well be true, but it's somewhat difficult to falsify; you can always posit an effect that only appears in the small statistically-underpow

This hypothesis could well be true, but it's somewhat difficult to falsify; you can always posit an effect that only appears in the small statistically-underpowered cohort that Scott sampled, and which would be swamped by the average of the population as you start to increase the sample size to verify the effect. As a counterpoint, Scott went the other direction in his post, arguing that the true effect was more general, but the metrics previous academics used was broken, and therefore undersold the strength of the effect they were detecting: > I think the most likely explanation is that tests for Openness have limited validity, which makes the correlation look smaller than it really is. If being an eldest sibling increases true underlying Openness by a lot, but your score on psychometric tests for Openness only correlates modestly with true underlying Openness, that would look like being an eldest sibling only increasing test-measured-Openness a little bit. It's simple to falsify this (though it requires some work); just do more experiments on the general population using the metric that Scott likes [1], and see if that detects a stronger birth-order effect. [1]: https://www.researchgate.net/publication/230787941_Construct_validation_using_multitrait-multimethod-twin_data_The_case_of_a_General_Factor_of_Personality https://www.researchgate.net/publication/230787941_Construct...