OF ALL THE demographic divisions among America’s Democrats and Republicans, few are as wide or as deep as the educational divide. Consider how white voters cast their ballots in the 2016 presidential election. Some 64% of non-college-educated whites plumped for Donald Trump. Among those with a university degree, the figure was just 38%. Congressional elections feature a similar split: a recent analysis by the Wall Street Journal found that of the 30 House districts with the highest concentration of college-educated voters, all but three are represented by Democrats.

This educational divide is caused in part by changing political attitudes. A survey conducted in 2015 by the Pew Research Centre, a think-tank, found that 24% of Americans with a university degree held consistently liberal positions on a range of political issues—including government performance, the social safety-net, the environment and immigration—up from 5% two decades ago. For those who had studied in graduate school, the figure was 31%. Of Americans without a degree, just 5% held such liberal opinions.

Is university education itself behind these left-wing political views? Or are individuals with liberal values more inclined to attend university in the first place? In a speech in 2017 at the Conservative Political Action Conference, an annual shindig for conservative activists, Betsy DeVos, the education secretary, accused American professors of telling their students “what to do, what to say and, more ominously, what to think.” This view is surprisingly common. A survey by the Pew Research Centre in 2018 found that, of the nearly two-thirds of Americans who were dissatisfied with the country’s universities, roughly half (79% of Republicans and 17% of Democrats) thought that a “major reason” for their shortcomings is that professors bring their political and social views into the lecture hall.

An unpublished analysis by Shom Mazumder, a PhD student in government at Harvard University, which was shared with The Economist, suggests that academia’s indoctrination of America’s youth has not been as successful as Ms DeVos claims. Mr Mazumder’s study is based on data from the Co-operative Congressional Election Study (CCES), a poll of more than 50,000 people led by researchers from Harvard and Tufts universities. One of the advantages of this survey is that it tracks the same respondents over time, asking them about their educational attainment as well as eliciting various opinions on political and social issues.

Mr Mazumder found little evidence that college education itself makes people more liberal. Between 2010 and 2014, survey respondents were asked every year which political party they identified with. The share identifying as Democrats did not shift significantly between freshman year and graduation. Similarly, when asked about their political viewpoints, the share of students identifying as conservative changed little during their time at university. The same pattern held for questions about climate change, health care and immigration (see chart). This suggests that colleges simply attract students with pre-existing left-wing dispositions, rather than changing their ideologies once they arrive.

Although the survey responses oscillated from year to year, the effects were not big enough to be statistically significant. Such a lack of evidence should discourage people from believing that academic elites push their left-wing agenda onto their impressionable young pupils. But given how often conservative-leaning media rail against leftist indoctrination in universities, it almost certainly will not.