Whoa. I didn't know that part; I thought maybe geography had something to do with rates.
The insurance company looks at how many docs have lawsuits based on a particular specialty, what the issue was, what the chances are that the same problem will happen again, etc. It's a statistical thing. There aren't that many companies that will write malpractice insurance.
My stepmother was an agent in an independent office in Illinois, and they rep'd for a company that did write medical malpractice insurance. She worked up until the day she died, almost 20 years ago, and even back then, it was particularly tough on small town docs, because they couldn't afford their insurance. Or if they could, they only took out minimal coverage.
The problem is not just incompetence in doctors for such high rates, due to the increase in lawsuits. It's the suit happy ambulance chasers who advertise on tv and who take a minimum of 1/3 of the amount received, but even more so...it's the insurance companies who are willing to pay out without much investigation on the theory that settling out of court most likely will cost less than defending the doctor and running the risk of a jury settlement and paying court costs and attorney fees.
I think I've mentioned before, the ex was sued back when we were still married. The patient not only didn't follow post-op instructions but also did not come in for follow up appointments, because he decided he didn't need to. Fortunately the ex documented everything. Patient ended up with severe complications, resulting in more surgery. He went and got a lawyer and filed a lawsuit. Malpractice company appointed lawyer meets with ex and tells him, insurance company will pay this guy x number of dollars and this will all go away, all you have to do is sign on the dotted line. Ex said no, he didn't do anything wrong and wanted to take it to court. Attorney tried to talk him out of it. Ex stayed firm. Upshot was....judge threw it out of court, no grounds for the lawsuit. If ex had signed on the dotted line, not only would his insurance have shot up like a rocket, but some guy would have gotten several hundred thousand for no reason!!!!!
Most surgery specialties - especially plastic, anaesthesia, OB/GYN... have the highest rates.
It took my parents 4 YEARS to find an attorney who would file a malpractice suit against the doctor, and the hospital, for me getting badly burned by the hot water bottle they laid me up against right after I was born.