For me the interesting part is that it's bimodal, because it tells us about the characteristics of the centre. It's not just simply an IQ curve since in that case you'd be unlikely to get such a strong refusal from high school dropouts compared to masters degrees. The kind most likely to respond to the messaging - which has all been appeals to authority, appeals to morality, appeals to shame and outward perception - seem to be the same kind who place value on academic qualifications and think they reflect a person's value.

PhDs are least susceptible possibly less because of their IQ and more because they're the participants in academia who see it for what it really is, having gone through it all. In that sense I wouldn't be surprised if there's not much difference in signal regardless of the type of PhD, since those possessing bullshit qualifications are well poised to know how worthless they really are.

But more realistically you would probably see a disparity, since the non-STEM, African Dance Therapy type PhDs probably correspond to political affiliation, which does produce a clear signal in propaganda susceptibility.