Bryan Caplanhas six “rules for optimizing your family size” which concludes with this:

When you’re on the fence, err on the side of having another kid. A life well-lived includes achievement as well as happiness. Creating and raising one more child is a great achievement, even your last child makes you marginally less happy.

A year ago, I reviewed Caplan’s Selfish Reasons to Have More Kids: Why Being a Great Parent is Less Work and More Fun Than You Think for The Interim and despite the seemingly negative conclusion, it would still probably rate as one of the best ten books I’ve read in the past decade. Of course, I whole-heartedly endorse his pro-natalism.