Fight Me, Psychologists: Birth Order Effects Exist And Are Very Strong

Original research. Noticing that rationalist/transhumanist crowds skew firstborn, Scott added birth-order questions to the SSC survey (7,248 usable). Controlling rigorously within family size (the confound prior studies botched), among two-child families 71.4% of respondents are the elder (p ≤ 1e-8); the skew holds across family sizes and is a LARGE effect (bigger than the sample's racial or many gender gaps). Pop-psych birth-order claims (conservatism/rebelliousness) don't replicate, but Rohrer et al (2015) found tiny effects on IQ and Openness/Intellect; Scott argues the true effect on intellectual curiosity is much larger than measured (test-validity attenuation), which would explain the firstborn skew. Speculates on mechanism (parenting time conflicts with behavioral genetics; immune effects), calls for follow-up, and posts the data.

Quality 75 · Excellent. Excellent floor. A striking, careful, much-cited piece of original research; the within-family-size control is the key methodological fix prior work missed, the effect is large and robust, and the Openness/Intellect mechanism analysis is honest about its scale problem. Held at the Excellent floor as a focused single-finding survey study with an unresolved mechanism.

Claude’s paradigm shift 58 · Moderate. Moderate–Notable (58). A genuinely fresh, striking empirical contribution — the within-family-size birth-order skew in intellectual communities, a large effect that family-size-confounded prior studies missed.

Real-world impact 3 · Moderate. Moderate (3). The canonical 'rationalists/intellectuals skew firstborn' reference; it moved the birth-order discussion (Rohrer herself responded, Sandel's classroom anecdote) — real niche/professional influence, no material change.