A study on couples' retirement transitions found that women who took new jobs after retiring from their primary careers reported high marital satisfaction, more than when retiring completely.
A study on couples' retirement transitions found that women who took new jobs after retiring from their primary careers reported high marital satisfaction, more so than those who retired completely.
It is an idiom which is used when making a comparison using a "more than" type and when you also want to refer to a previously mentioned verb/action. In your case, the word "so" refers to "reported high marital satisfaction."
here it goes, I would like to give an extra sentence. a study found that woman who took new jobs after retiring from their primary careers reported higher marital satisfaction than those who retired completedly. So here "so" refers to a status, it is like "he is more active". "So" is active