WellPoint Inc. holds an overwhelming share of the commercial health insurance market in 13 of Indiana’s 14 largest metros, according to a controversial new study by the American Medical Association.

The report, issued Nov. 28, concludes that Indianapolis-based WellPoint has 56 percent of all Hoosiers enrolled in either employer-sponsored or individually purchased medical policies. The nearest competitor, according to the study, is Minnesota-based UnitedHealthcare, with 12 percent of the statewide commercial market.

The AMA study is based on data collected via surveys by Tennessee-based market research firm HealthLeaders-InterStudy in 2010. It includes enrollment for all types of plans, including PPOs, HMOs, consumer-directed health and point-of-service.

But it fails to include all members of health plans at self-funded employers, according to a critique of the study by the health insurance trade association, American’s Health Insurance Plans. WellPoint referred questions about the AMA study to AHIP.

“Most critically, the data are incomplete and omit various competitive alternatives, with the result that the market share figures do not reliably reflect the actual state of competition in such markets,” AHIP staff members wrote in response to the U.S. Department of Justice about the AMA data.

AHIP‘s concern is to point out that it is the rapid consolidation of hospitals and doctors that is the biggest threat to controlling health care prices. There is some local evidence for that.

But the American Medical Association data still show, either due to market dominance or superior pricing and products, WellPoint holds more than quadruple the number of commercial customers than UnitedHealthcare. And in some markets, the gaps are even wider. Only in Lafayette does UnitedHealthcare come close to WellPoint’s shares.

Here are the market shares for WellPoint and its nearest competitor, shown in the AMA study in Indiana’s 14 largest metropolitan areas. The data include Hoosiers enrolled in any WellPoint health plans, even if that plan is operated out of a different state.

Indianapolis: WellPoint, 59 percent; UnitedHealthcare, 12 percent
Anderson: WellPoint, 68 percent; UnitedHealthcare, 9 percent
Bloomington: WellPoint, 59 percent; Aetna Inc., 16 percent
Columbus: WellPoint, 61 percent; SIHO Insurance Services, 16 percent
Elkhart-Goshen: WellPoint, 63 percent; Cigna Corp., 8 percent
Evansville: WellPoint, 44 percent; Welborn Health Plans, 18 percent
Fort Wayne: WellPoint, 53 percent; Aetna, 15 percent
Gary: WellPoint, 48 percent; UnitedHealthcare, 20 percent
Kokomo: WellPoint, 57 percent; Advantage Health Solutions Inc., 13 percent
Lafayette: WellPoint, 40 percent; UnitedHealthcare, 27 percent
Michigan City-LaPorte: WellPoint, 61 percent; UnitedHealthcare, 11 percent
Muncie: WellPoint, 65 percent; UnitedHealthcare, 9 percent
South Bend-Mishawaka: WellPoint, 42 percent; Blue Cross Blue Shield of Michigan, 20 percent
Terre Haute: WellPoint, 73 percent; UnitedHealthcare, 10 percent