In the Medscape Insurer Ratings Report 2011, physicians listed the companies with the greatest frequency of denials, with United Healthcare at the front of the pack. The responses were collected from 10,214 physician surveys and included only those that specified a specific answer. Here are 11 statistics about who gives physicians the highest denial rate:

The National Health Insurer Report Card released data on Aetna, Anthem Blue Cross Blue Shield, Cigna, Health Care Service Corporation, Humana, Regence, UnitedHealthcare and Medicare. The data was gathered from 380 physician practices between February and March 2012.

Health insurers are paying physicians seven days faster and denying 12-18 percent fewer claims than the year before, according to a release by Athenahealth.

UnitedHealth Group, Healthspring, Coventry Health Care and Humana are among the insurers that will receive the same payment rates for 2011 as they did this year for administering Medicare Advantage plans, according to a report in Bloomberg BusinessWeek.

All but one of the nation's largest health insurers reported significant commercial enrollment losses in 2009 and all of them are cautious about growth in 2010, according to the insurers' recently issued annual reports.

Lobbying disclosure reports show that that the health insurance lobby increased spending by 24 percent in 2009, as Congress debated health reform legislation, according to The Hill.