Six major U.S. health care systems announced on Wednesday a nationwide data-sharing collaborative in cooperation with the Dartmouth Institute for Health Policy and Clinical Practice, to help curb health care costs and improve outcomes.

The group, which includes the Cleveland Clinic, Dartmouth-Hitchcock, Denver Health, Geisinger Health System, Intermountain Healthcare and Mayo Clinic, manages a total patient population of nearly 10 million.

The collaborative said it will first tackle eight conditions or treatments with rising costs and widespread regional variations in outcomes. The first project is total knee replacement, a surgery performed more than 300,000 times a year, which carries a $16,000 to $24,000 price tag. Diabetes and heart failure analyses will start next year.

"If we know that the treatment path for diabetes at one institution results in better clinical outcomes, higher patient satisfaction, and lower overall costs, then there is knowledge to be shared and replicated in other institutions," Mayo Clinic's CEO Dr. Robert Nesse said in prepared remarks.

Dartmouth Institute, which will help handle the data analysis, is best known for studies showing how cost and quality of medical procedures -- often not going hand-in-hand -- vary widely across the country.