This is big when it comes out in Nature.
"Part of the pay discrepancy is that graduate students are classified as part-time workers who, on paper, do only 20 hours of work per week, with the rest of the time devoted to their studies. But for many, this does not reflect reality. ...says that she had classes as part of her programme for only the first two years, and she’s been doing research full time for the past three. ...a neuroscience graduate student at UC San Diego, says that every single graduate student they know works more than 40 hours per week."