deepz, the statement you are using about the national practitioner data bank is a gross distortion that was used by the AANA in 1998/1999. If you look at the national practitioner data bank reports (available at
http://www.npdb-hipdb.com) you can see for yourself. The AANA reports that MDAs had 7x more suits than CRNAs over 7 years (3500 vs 425). However, this is incorrect since they lumped ALL physicians with anesthesia-related complications into that number of 3500 (which include anesthesia-related complications in offices performed by plastic surgeons, in ERs by ER docs, etc...). What further blurs those numbers is that the numbers represent numbers of reports that led to payments - and does not reflect the number of reports of suits brought agains MDAs vs CRNAs.
The incongruity between MDA and CRNA malpractice premiums, is that most states (due to very successful trial lawyer lobbyists) require a minimum coverage for physicians... While in some states physicians can choose to opt-out and go "bare", most states dictate a minimum of 5million dollars of coverage up to a minimum of 10million dollars of coverage (primarily to help with "tail" coverage - ie: you do a general anesthetic for a crashing c-section, you could technically be brought to court for medical complications of the child during the child's first 18 years of life - which some lawyers may pin on the anesthesia as well as the OB). So what has happened is that trial lawyers have become more and more successful at getting high damages and thus really hurting the insurance companies. Most have closed down, and there are very few medical malpractice companies left - and they can now dictate even higher premiums for high coverage. There are no such "requirement" laws for advanced practice nurses (yet...), and therefore, they are relatively cheaper to cover.
The average malpractice premium, depending on length of practice, number of suits in last 3/7 years, and type of practice (pain management adds more) is between $45,000 (primarily seen in states where tort-reform and caps have passed: ie: california) and $85-95,000 (florida for now).
the difference in insurance has absolutely nothing to do with responsibilities: because it doesn't matter if you cover 4 rooms vs 1 room. However, i would agree that the risk of being sued increases by the number of cases done per day.... but the insurance companies don't look at that when they decide premiums.