I'm allowing for confirmation bias. When I see other people who said they didn't want kids and then didn't change their mind, this affirms my own experience, so I'm more likely to see this as the norm. ford_prefect42 sees the opposite as confirmation that his experience is the typical one. My rough guess is that it's probably somewhere around 50/50; but then I usually place odds of things at 50/50 when I've seen some of each thing, and of course those numbers are at least somewhat inaccurate.