It is no secret that the cost and quality of health care can vary greatly within a state as large as California. But by how much?

A new online tool made public Wednesday aims to quantify those variations to help policymakers and health care providers improve the health of Californians.

The California Regional Health Care Cost & Quality Atlas crunches 2013 data on medical care provided to about 24 million people — some two-thirds of the state’s population. It also includes information on care afforded by different types of coverage, including commercial health insurance, Medicare Advantage and Medi-Cal, California’s Medicaid program for the poor.

Among the findings:

• Orange County has the highest breast cancer screening rate among Medi-Cal managed care enrollees, at 66.4 percent. The lowest screening rate for that group of patients, in the Greater Fresno area, is 44.2 percent.
• If all commercially insured Californians received the same quality of care offered in top-performing regions, nearly 200,000 more people would have been screened for colorectal cancer and 50,000 more women would have been screened for breast cancer.
• Northern California tends to outperform Central and Southern California in quality of care for cancer, diabetes and asthma.
• The lowest performing region for health care quality covers Mono and Inyo counties in Central California; the highest is Contra Costa County.

The Atlas was developed by the Integrated Healthcare Association (IHA) in partnership with the California Health and Human Services Agency and the California Health Care Foundation. (California Healthline is an editorially independent publication of the California Health Care Foundation.)

Although the Atlas is based on data collected the year before the rollout of the Affordable Care Act, it is nonetheless one of the most comprehensive data sets currently available, said Jeffrey Rideout, president and CEO of IHA.

IHA plans next year to update the Atlas with 2015 data, which will allow for comparisons of health care provided after the coverage-expanding provisions of the Affordable Care Act took effect.

“The breadth of this information is very important,” Rideout said. “By highlighting variation in health care quality and costs across California, the Atlas pinpoints opportunities not only to provide better care but lower costs.”

The Atlas shows that if care for everyone were provided at the same cost as in San Diego — deemed a relatively inexpensive and high-quality region — the overall cost of care across the state would decrease by an estimated $4.4 billion annually.

One of the most interesting findings from the Atlas is the consistency with which HMO plans outperform preferred provider organizations (PPOs), said Cheryl Damberg, a health care cost expert at Rand Corp., a Santa Monica-based think tank.

According to the Atlas, commercial HMOs outperform commercial PPOs on five of the six clinical quality measures while also providing cheaper care. The difference in the cost of similar care between HMOs and PPOs is estimated at $210 per enrollee annually.

“That’s a real testament to those (HMO) organizations being held accountable and working hard to improve,” Damberg said. “These results would signal that clearly they’re doing a better job at delivering better quality of service.”