What medical opinions are recognized in social security cases?

Medical opinions of three types of medical sources are recognized in social security cases: "(1) those who treat the claimant (treating physicians); (2) those who examine but do not treat the claimant (examining physicians); and (3) those who neither examine nor treat the claimant (nonexamining physicians)." Lester v. Chater, 81 F.3d 821, 830 (9th Cir. 1995). Generally, a treating physician's opinion should be accorded more weight than opinions of doctors who did not treat the claimant, and an examining physician's opinion is entitled to greater weight than a non-examining physician's opinion. Id. Where a treating or examining physician's opinion is uncontradicted by another doctor, the Commissioner must provide "clear and convincing" reasons for rejecting the treating physician's ultimate conclusions. Id.