Have there been any studies on the affect birth order has on enneagram type? For instance... an eldest child might be more likely to be an 8, an only child a 4 or 5, a youngest child a 3, a middle child a 9, someone who is significantly older or younger than the rest of his/her siblings a 6, an only girl in a large family a 2, an only boy in a large family a 7, etc.