Yes, there are such studies, quite a few IIRC (there have been some deep threads on this topic here on HN before, I’ll see if I can dig any up), and there definitely is some component of education providing higher earnings purely due to employer selection, and/or social selection & bias. So earnings are a mix of the education and skills learned, and of the social signaling that the certificate provides, plus other causes. I’m also in full support of education, but you’re right the disclaimer is absolutely necessary, and there are some components of misleading social narrative surrounding education, just like there are surrounding social mobility.