"On the margin, you should consider having more kids. If you were planning to have zero kids, consider having one. If you were planning to have 3 kids, consider 4, etc." Wait, I thought happiness research indicates that the step from zero to one is a decrease in happiness whereas the step from, say, 3 to 4 would be only a negligible decrease in happiness. So there's that asymmetry, if I remember one of Caplan's blog posts correctly.