This answer to a question about "leftist" academia led me to wonder if the observed tendency towards more progressive and liberal views in more educated people is a product of a chance drift in the Overton Window within academia, or whether there is an actual causative mechanism here.
One way to address this would be to compare this trend between subjects. Subjects in the Humanities often have an unavoidable socio-economic component (e.g. history, human geography, economics), so in these subjects students will be exposed to the political views of their professors, and academic advancement for those with opposing political views will be harder. Meanwhile in the STEM subjects this is much less true.
So if the leftward trend of the educated is merely due to selective recruitment and indoctrination into a leftist subculture then we would expect to see the effect restricted to the humanities, with graduates and faculty in the STEM subjects being much less affected. OTOH if it is actually education that is correlated with progressive views (by whatever mechanism) then we would expect STEM graduates to have similar politics to the humanities.
Has any research been done which analyses the politics of university graduates by subject?