Monday, January 05, 2009

Sibs and offspring:  Reading R.A. Fisher's ideas about the heritability of fertility as summarized by David B. over at Gene Expression, it made me wonder to what extent your own completed family size is associated with that of your parents.  I was surprised to find that, according to GSS data, it's only .13. People depart from their parents more than I thought.  

To look at it in a more detailed way, here is the distribution of completed family size for people who grew up with two siblings:

Percent in each category

No children 17.2
One 12.2
Two 29.9
Three 19.9
Four 10.4
Five  4.7
Six 2.5
Seven 1.4
Eight or more 1.8

The modal category is two children, so the tendency here is more to follow the current norm of two kids rather than to imitate one's parents.  People are really all over the place here. 

I also wondered if the correlation has changed at all over the past six decades, but I saw no evidence for it.  It doesn't seem to vary across gender either.  


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