Here is a form of study I have seen in various guises over the years: The authors are interested in the question of whether people in a society are becoming more “polarized” in their attitudes in some kind of global sense. So what do they do?
1. Find data that has a long repeated series on a variety of attitudes.
2. Select those items that have been continued in these data over a long period.
3. Look at whether responses to these items are more divergent now, or more divergent for some group, than they used to be.
For me, here’s the problem: questions only initially appear and stay on public opinion surveys so long as disagreement is sustained in the population. Imagine if we had really long time series on public opinion. Do you believe women should be allowed to vote? Do you believe alcohol should be outlawed? Do you think our state should secede? Do you believe fugitive slaves should be returned to their masters? Or, obversely: Do you think gay couples should be allowed to get married? Do you think people should be allowed to smoke in public places?
So it seems like the study is strongly biased against finding evidence of polarization from the get-go, especially given that I think it’s less likely for questions without disagreement to be asked in the first place then for them to be re-asked for comparative purposes later on. More speculatively, I would not be surprised if there is also a bias toward finding evidence of more highly educated people being leaders of public opinion, because I would bet that questions with low overall disagreement are more likely to make it onto surveys if there is more disagreement among elites than there is among the masses.