Poor pay for rank-and-file academics is such an established fact of life that seldom do we stop and wonder why.

One economist made it the subject of a new research paper. He found that, on average, professors earn about 15 percent less compared with their equally educated peers when controlling for outside factors.

Why?

In the paper, and in an interview with The Chronicle, the paper’s author, Daniel S. Hamermesh, a professor of economics at Barnard College, explained that five percentage points of that 15-percent disparity can be attributed to the flexible scheduling that comes with an academic life. Yes, professors work at night and often on the weekend, but the work is distributed throughout the week more evenly than, say, that of a doctor or a lawyer.

Mr. Hamermesh said his analysis relies on the idea that two things make people happy: the time they have outside work for leisure and the things they can buy to use in that time.

“The beauty of the academic life is on each day, on average, I have more leisure time because I have more leisure time on weekdays,” he said. “I'm not working quite as hard. And I don't have so much leisure time on the weekends. I'm working harder. Coupling that with the things I buy, and making some reasonable assumptions based on the literature about how these things are valued by people — that's where I get 5 percent.”

As part of his research, Mr. Hamermesh asked economists in a survey to describe the reasons they enjoy their jobs. Flexibility of scheduling was outranked only by their love of research, their love of teaching, and interacting with colleagues.

“So are we undervalued?” Mr. Hamermesh said. “Yeah, we all want more money. On the other hand, we get something in exchange for that loss of money. All these freedoms, one of which is the flexibility of scheduling, which I document does matter here.”

John Ziker, a professor of anthropology at Boise State University, is in the middle of a study of how professors use their time and has published on the topic in the past. He too agrees that faculty members have flexibility in when they work, but he argues the pay disparity pointed out by Mr. Hamermesh could be attributed to how the public values higher education.

Much of academic work, he said, is invisible to the public, and it’s a common misperception that professors have plenty of  leisure time. In his earlier study, he found professors worked about 60 hours a week.

Another challenge, according to Mr. Ziker: Professors don’t charge billable hours or minutes.

“What I am aiming at here is the public doesn’t value higher education as much as they value these other doctors and lawyers,” Mr. Ziker said. “That’s why there is a difference. It’s because we’re not valued as much.”

Chris Quintana is a breaking-news reporter. Follow him on Twitter @cquintanadc or email him at chris.quintana@chronicle.com.