Many insurers are offering smaller networks of doctors in their Medicare Advantage and commercial health plans this year. But those networks may be even narrower than they seem, physicians and regulators say, because the lists often include names and addresses that are erroneous or out-of-date. In some cases, the doctors shown as participating in plans have moved, retired or died, surveys show. Others are listed under the wrong specialty, work in hospitals full-time and don't see outpatients, or don't accept the plan being offered. In a study published in JAMA Dermatology last month, researchers at the University of California, San Francisco, tried contacting all 4,754 dermatologists listed in the three largest Medicare Advantage plans in 12 metro areas. [Subscription Required]