"Single-parent households" in Scandinavia doesn't mean the same thing as it does in most of the world. There is usually still a high degree of coparenting.
I almost noted in my prior comment that income is the second biggest factor but left that out. Totally agree that income is a big part of the equation. I also bet because it's Sweden it also has to do with public services like childcare being available.
I am on my phone but you can Google and find lots of data that shows dual parent/intact families correlate positively with a bunch of other factors like income, college graduation, etc. More parents=more resources. More resources is generally better than less. Having kids myself, I can barely imagine being able to do it by myself... and even if I could it would certainly be to a lesser quality.
