For an effect this prevalent and strong my first reaction is "check your data." Then I read this: >It’s unlikely that age alone is driving these results. In si

For an effect this prevalent and strong my first reaction is "check your data." Then I read this: >It’s unlikely that age alone is driving these results. In sibships of two, older siblings on average were only about one year older than younger siblings. And I really start thinking you have to check your data. The average age difference in that cohort is only one year and humans have a 9 month gestation. Something is likely wrong with your data or your sample.