A trio of labour economists suggest that effort at work is correlated with race.Given the long history of making racial slurs about the efforts of some workers, any study casting black and Hispanic men as lazier than whites and Asians is sure to court controversy.

A provocative new working paper by economists Daniel Hamermesh, Katie Genadek and Michael Burda sticks a tentative toe into these murky waters.They suggest that America’s well-documented racial wage gap is overstated by 10% because minorities, especially men, spend larger portions of their workdays not actually working.After rejecting a number of plausible explanations for why this might be, the authors finally attribute the discrepancy to unexplained “cultural differences”.

Acutely aware of the sensitivity of these findings, the professors delayed publication until after the presidential election.“I knew full well that Trump and his minions would use it as a propaganda piece,” says Mr Hamermesh, a colourful and respected labour economist.The paper may yet be seized on by those who are keen to root out “political correctness” and are perennially unhappy with current anti-discrimination laws.The study's method is straightforward.The data come from nearly 36,000 “daily diaries”, self-reporting on how Americans spent their working hours, collected from 2003 to 2012.Relying on the assumption that workers are equally honest in admitting sloth, the authors calculate the fraction of time spent not working while on the job—spent relaxing or eating, say—and find that it varies by race to a small but statistically significant degree.

The gap remains, albeit in weaker form, even with the addition of extensive controls for geography, industry and union status, among others.Non-white male workers spend an additional 1.1% of the day not working while on the job, or an extra five minutes per day.Assuming their controls are adequate, that would still leave 90% of the wage difference between white workers and ethnic minorities, which was recently estimated to be 14%, unexplained.This could conceivably be the product of discrimination, or of something else.Digging out the cause of this curious gap remains hazardous.Worse treatment by managers of minority workers may itself encourage slacking, says Philip Cohen, a sociologist at the University of Maryland.
The authors argue that this point is moot, since self-employed minority workers show similar behaviour, but the difference is not statistically significant.

A recent experimental approach, in which cashiers in French grocers’ shops were randomly assigned to more- or less-biased managers, saw greater absences and more sluggish scanning when working under the unfair bosses.It found that eliminating manager bias would increase time spent at work by minorities by an estimated 2.5%.Uncomfortable though the topic may be, the authors have attempted a rigorous analysis.Denunciations came quickly, however.

Within hours of publication, Mr Hamermesh received vitriolic messages and was labelled a racist in an online forum popular among economists.Mr Hamermesh, an avowed progressive, who refers to Donald Trump only by amusing nicknames and resigned from a post at the University of Texas over a state law permitting the open carrying of firearms, finds this unfair.He notes that Americans work too much.His preferred solution would not be for some groups to work more, but for others to work less.