7. I plan to confirm or disprove, once and for all,     
    whether our community has more older siblings. For lack 
    of a fancier way to do this, I’ll take the set of all 
    people who have exactly one sibling, and see what 
    percent of them are older vs. younger. If it’s 
    significantly above 50% older, I’m going to interpret 
    this as a birth order effect. I’ll do the same with the 
    set of people who have two siblings, three siblings, 
    etc, and combine them all for a final determination. 
    Half-siblings will be ignored. If you have any problems 
    with this methodology, tell me now.

But I checked the data I received before and after I posted that, and the birth order effects are about equally strong throughout.

Of the before-posting people, 2199 had exactly one sibling, and 71.1% of those were the older.

Of the after-posting people, 776 had exactly one sibling, and 72.3% of those were older.

A t-test revealed no difference between the two groups, p = 0.527.