Yep, but just about everything about parenting is anecdotal -- there's such a tiny amount of actionable data out there. But then you have kids, and you have to

Yep, but just about everything about parenting is anecdotal -- there's such a tiny amount of actionable data out there. But then you have kids, and you have to take a lot of action... so hunches, intuition, and anecdotes play a huge role. I think you are right, the sleep deprivation is the biggest thing -- and that is what I was forewarned about by other parents, and certainly my experience bore that out (my kids are 3 and 0.75 years old). I am sure you could do a study of you found a cohort of people who for some other reason were similarly sleep deprived, and you would probably see similar negative net happiness.