No one disputes that American academia is decidedly more liberal than the rest of the population, or that there is a detectable shift to the left among students during their college years. Still, both studies in the peer-reviewed PS, for example, found that changes in political ideology could not be attributed to proselytizing professors but rather to general trends among that age group. As Mack D. Mariani at Xavier University and Gordon J. Hewitt at Hamilton College write in the current issue, “Student political orientation does not change for a majority of students while in college, and for those that do change there is evidence that other factors have an effect on that change, such as gender and socioeconomic status.”

That may be, said Daniel Klein, an economist at George Mason, but those results don’t necessarily mean there isn’t a problem. Mr. Klein, whose research has shown that registered Democrats vastly outnumber Republicans among faculty in the humanities and social sciences at American colleges and universities, maintains that the focus on the liberal-conservative split is misdirected. Such terms are vague and can be used to describe everything from attitudes about religion and family to the arts and lifestyles, he said.

The real issue, said Mr. Klein, who calls himself a libertarian, is that social democratic ideas dominate universities  ideas that play down the importance of the individual and promote government intervention.

Such “academic groupthink” means that the works of such thinkers are not offered enough, he argues. “A major tragedy is that they’re not getting exposed to the good stuff,” he said, citing the works of John Stuart Mill, Adam Smith, Friedrich Hayek and Milton Friedman.

“Even if we had hard, definite evidence that students weren’t influenced by their professors, there is still reason for great concern about the composition of the faculty,” Mr. Klein added.

K. C. Johnson, a historian at the City University of New York, characterizes the problem as pedagogical, not political. Entire fields of study, from traditional literary analysis to political and military history, are simply not widely taught anymore, Mr. Johnson contended: “Even students who want to learn don’t have the opportunity because there are no specialists on the faculty to take courses from.”

“The conservative critics are inventing a straw man that doesn’t exist and are missing the real problem that does,” he added.