Outliers: The Story of Success · chapter 1 · id outliers-c1-08-birth-seasonality-is-not-perfe
“Birth seasonality is not perfectly uniform across quarters -- actual birth distributions vary by country and era, with summer months typically having slightly higher birth rates, which weakens the 25%-per-quarter baseline Gladwell uses.”
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Birth rates are not evenly distributed across months. In many countries, summer and early fall months see slightly higher birth rates, meaning the expected distribution is not exactly 25% per quarter.
Buckles & Hungerman (2013), Demography 50(5)FLAGGED: DOI not in registry
Birth seasonality varies significantly -- winter births are more common among younger and less-educated mothers. Using uniform 25% per quarter as a baseline introduces systematic error.
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