STUDENTS may be reluctant to speak up in class, but they are more than happy to express their views of their teachers anonymously online. That provides a potentially useful pool of data. With assistance from Enrico Bertini and Cristian Felix of New York University, The Economist has analysed 1,289,407 reviews of 1,066 professors and lecturers in New York state.

Most of the commentary is innocuous: professors are praised for their brilliance and generosity, and admonished for being boring or tough graders: “This prof makes u work your butt off but u still won’t get an A”. But the outliers are startling. One student complained of a professor who resembled “one of those worm guys who is always drinkin coffee” from the film “Men in Black”. More flatteringly, an adoring student termed her teacher “a philosophy love-God”, and remarked that her life’s goal was to “become the mother of his million intellectual babies”.

Students assign grades based on three criteria: “helpfulness”, “clarity” and “easiness” (the diligence and brainpower of the teachers apparently count as less relevant). Professors tend to receive good marks in the first two categories, averaging 3.7 out of 5 for both categories, but slightly lower marks for “easiness”. This is in part because the perceived difficulty of courses varies so much by discipline: in general, academics teaching quantitative subjects tended to receive lower ratings for ease. Sociologists earned an average easiness rating of 3.4 out of 5, notably higher than the 2.9 earned by physicists. Philosophy is boring, but (or therefore) its teachers count as brilliant.

Teachers could also benefit from a bit more of the scrupulous attention paid on modern campuses to sexual equality. Earlier analysis by Ben Schmidt of Northeastern University showed that the language used to describe professors was heavily gender-dependent. Men were more likely than women to be described as “intelligent” or “funny”, but less likely to be described as “nice” or “mean”.

Even dire ratings aren’t necessarily condemnations of teaching ability: one study from 2007 found that professors’ overall ratings were significantly correlated with both how easy their courses were and how attractive they were perceived to be, while another study from last year found that mathematics professors with Asian surnames tended to receive poorer reviews because students had difficulty with their accents. Professorial brilliance is too intangible to distil into a single score. Not that anyone would do that to students.