It’s no surprise that Thomas H. Benton’s column on why you shouldn’t go to grad school is one of the most popular articles on The Chronicle‘s Web site these days, what with the bottom dropping out of the humanities job market and all. Now, via The Boston Globe‘s Braniac blog, comes one more reason to think twice about getting a doctoral degree: According to the economics blogger Mike Mandel, the real earnings of full-time workers who hold a Ph.D. have sunk by 10 percent since 1999 (see chart below).