As far as marriage is better, regression will show that shared child rearing (less load per person) and higher resources are the primary reasons for it (IIRC) being better. This can be contrasted with Asian cultures where children are raised by entire families.
The opposite, showing that unmarried is inferior, needs to be adjusted for personalities of people who cannot cope in marriage as well as the impact of becoming separated due to becoming pregnant (ie: unwilling to focus). A rather complicated situation.
Marriage is a great signal for showing the parents dependability. It's inherent value is... somewhat lower.