J. Paul Leigh at the University of California in Davis has taken one of the most in depth - and most recent - looks at what doctors earn. He finds that over a lifetime, a primary care doctor can expect to make $1.5 million less than a medical school classmate who goes into specialty care - and $2.8 million less than a doctor in the best-paid specialty, neurological surgery.

Here's the full chart of how the earnings of various doctors stack up:

This aligns with previous research that has also shown a big pay gap between primary care doctors and specialists. (There is some variation, though, which may be a product of certain studies not accounting for variables like gender and payment during residency, which tends to be lower).

One big question this study raises is: How much does the pay gap matter to medical students? Research from the Graham Center found, perhaps surprisingly, that it might not factor in as much as we thought: Having higher student debt actually correlates with a higher likelihood of pursuing a primary care career. Debt-free doctors, the thinking goes, are more likely to come from a higher income background - and expect a higher salary. Those who accumulate debt to pursue a medical degree may have lower expectations - or put less emphasis on - their ultimate earnings.

More recent research on medical student decision-making suggests even more nuance to how doctors select their ultimate career path. Yeshiva University's Martha Grayson recently looked at students who entered medical school intending to pursue a career in primary care - and how much debt they accrued. Her research, published in the journal Medical Education, did find a relationship between debt and career choice: Students with more debt were more likely to shift their career path away from primary care.

"Compared with their peers who sustained PC [primary care] career goals, those who switched career goals anticipated more debt and attached greater value to income," Grayson concludes. "Moreover, the decision to switch was associated with a marked increase in income expectations of an average of US$75,153."

Her research suggests - much as would be expected - that money does indeed matter in career decision making.