If we assume that the likelihood of a pregnancy leading to a child who lives long enough to be in our records is independent of the child’s order / mother’s age, then I agree that that the effects on the average birth order and average family size of our cardinals should in some sense cancel. However, it should still increase the error bars on both numbers and therefor the uncertainty of any conclusion. And I’m not sure I’d expect survival to be independent of order.
If we assume that the likelihood of a pregnancy leading to a child who lives long enough to be in our records is independent of the child’s order / mother’s age, then I agree that that the effects on the average birth order and average family size of our cardinals should in some sense cancel. However, it should still increase the error bars on both numbers and therefor the uncertainty of any conclusion. And I’m not sure I’d expect survival to be independent of order.