It's very socially unacceptable to admit you regret having had your kids. Even to an anonymous stranger conducting a phone poll.
I am much more inclined to believe studies that ask for self-reported happiness and compare to life events / states like childlessness without directly asking "do you regret your kids". From what I understand, having children is negatively correlated with happiness in those sorts of studies.
Did you reply to the wrong comment? That's why the parent poster led with this quote from IFS:
> By the time the 2016 survey rolled around, fathers were 40% more likely than childless men to see themselves as very happy.
That part of the study is about the same fathers who are now aged 50-70 and whose children have generally left the house and are no longer children.
I guess if you see it as in investment for future happiness when you're old, you can interpret it as "children make you happy", but not if you prefer to be happy now and over the next ~18 years.
That's way too simplistic.
It's like saying college is an investment for when your old. You may have loved learning about new things, but still rather not have to do a bunch of meaningless homework assignments,
You can actually enjoy being a parent immediately and simultaneously not like all the sacrifices. IT's a deeper kind of commitment. For some people, it's the first time they have actually loved something more than themselves. It's hard to express.