Yes, but just being accredited by an institution as having been educated in a subject doesn't mean that you are qualified for a job. I'm not saying that it isn'

Yes, but just being accredited by an institution as having been educated in a subject doesn't mean that you are qualified for a job. I'm not saying that it isn't a valid indicator, just that it seems subjective and fuzzy. If some "over-educated" employees still happy and perhaps have substantially greater output than their "less-educated" counterparts, then there could be a significant enough ROI on their education to justify it. However, you can't differentiate those from the "over-educated" workers that are unhappy that would be more productive in other roles. This is why I think a work happiness index would be a better indicator of how well those that are employed are fairing.