Another oft-mentioned part of the medical malpractice puzzle is the flood of doctors leaving the system because they can no longer afford malpractice premiums. Here (as opposed to defensive medicine and the number of lawsuits) the picture is somewhat unclear. The number of doctors in practice has remained steady and even increased. But some areas of the country don't have enough doctors, especially regions with large population growth and rural areas. There isn't any direct evidence showing doctors are leaving practice because of malpractice rates. Nor is there research showing they aren't.
What's clear is the economics of physician supply and demand are at work in these trends, and in some places, malpractice premiums will have an effect on which doctors decide to stay in practice.
There was this saying in the 19th century that a doctor had a 50/50 chance of helping or hurting you. We've come quite far from those days, thanks in part to the vice-like grip physicians have historically kept on supply and demand. This stems from a number of reasons, including gaining professional credibility (and creating associations to grant it), preserving salaries, and excluding other types of medical practice (osteopathy, chiropractic, etc) from gaining respectability.
But these controls on the number of rears in med school seats any given year have helped retain a regionally fractured care system. Most doctors prefer to live in populated areas. Salaries are also higher in populated areas. And most doctors are able to find a position in said metropolitan areas, thus decreasing the likelihood that economic necessity will drive enough practitioners out to rural areas.
When it's already economically and emotionally unappealing to practice in rural areas, bloated malpractice premiums can act as a proverbial feather to tip someone off the edge of the cliff. Some doctors will leave their practices because of it. But is tort reform the answer? No. Using tort reform to get at the system's supply constraints is like only taking dessert out of your all-McDonald's diet to lose weight. You might lose a couple pounds, but the real problem is still there.
That said, one study found that states with caps on damages had a 3% increase in the number of doctors per capita, and states with other tort reforms had a decrease in doctors per capita. Not convincing research either way, except to say that a very slightly larger number of doctors will stay in practice with tort reform.
Either way, malpractice itself isn't enough of a problem to send doctors running, nor is tort reform enough of fix to attract them in droves. The malpractice/tort reform dichotomy is, however, a grand distraction in talking about the actual problems with medicine.