Sally Rockey, deputy director for extramural research at the US National Institutes of Health, addresses the question of "whether investigators that hold MDs or MD/PhDs are more or less likely to be funded than those investigators that hold PhDs."
Using funding rate data from 1998 to 2011, filtered by degrees, Rockey says, "Investigators with a PhD have a slightly lower funding rate than those with medical degrees, and this is consistent over time." She adds that "to keep these data in context, remember that about 30 percent of principal investigators hold MDs or MD/PhDs."