It could also be cultural differences, a selection bias in the participants, differing criteria for "success/productivity"... or a thousand other reasons, too.

It could also be cultural differences, a selection bias in the participants, differing criteria for "success/productivity"... or a thousand other reasons, too. It's easy to jump to a conclusion or speculate why a desired outcome wasn't the actual outcome; but the best you can probably say is you just don't know why one was a "success" and the other a "failure" and look for a study of the reasons for a given outcome. I find it rare that popular reporting gets to the nuance required to really understand a research outcome much less to ascribe plausible, grounded reasons for that outcome.