I'm going to say that study has a serious smell. I can't read any of the detail (no access), but look at the example graph for Danish mothers. It suggests tha

I'm going to say that study has a serious smell. I can't read any of the detail (no access), but look at the example graph for Danish mothers. It suggests that in 1965, the average time spent by a non-university-educated mother on childcare for an under 13 was less than 10 minutes. That's an extraordinary claim, and needs extraordinary evidence to back it up.