a donor should give all of his contributions to one charity, and not spread them among several. The logic is almost exactly the same.
No, the logic is not the same at all. In the charity case the logic is that your contribution is too small to change the relative marginal suffering level among charities - thus if children in Africa is the most pressing need before your first 100 dollar contribution it will also be the most pressing need after your contribution. In the child case it is much more likely that your contribution to the first child will eventually lower the marginal need of that child below that of your other children.Likewise, a parent with several children should confine his spending to one child and let the rest die off. The logic is exactly the same.
(Note that the model applies only when the reason you give is to assuage suffering which may not explain most charity and certainly not parental giving to their children.)
Alexander Tabarrok Department of Economics, MSN 1D3 George Mason University Fairfax, VA, 22030 Tel. 703-993-2314
Web Page: http://mason.gmu.edu/~atabarro/
Director of Research The Independent Institute 100 Swan Way Oakland, CA, 94621 Tel. 510-632-1366