Philadelphia has plenty of primary-care providers overall, but there is far less access to care in communities with the highest concentrations of African American residents, according to a new study.

While the general findings were not a surprise - highly segregated black (and, to a lesser extent, Hispanic) areas were known to have fewer medical practitioners - the difference was bigger than the researchers had expected. The effect was independent of neighborhood poverty rates, which turned out to be less significant than anticipated, although it is not clear why.

The results pointed to the limitations even of sweeping legislation such as President Obama's Affordable Care Act, which led to unprecedented reductions in the number of people without insurance.

"It is great that you have more health insurance," said Mariana Chilton, a professor at Drexel University's Dornsife School of Public Health who was not involved with the study, "but how does that help African American communities who don't have access" to doctors?

The new research, published online Monday in the journal Health Affairs, used mapping tools to combine statistics on primary-care provider locations with census data for adults that included insurance, income, race, and ethnicity. It used travel time - an estimated five minutes by car, or 1.4 street miles - as a proxy for geographic access, because public transit routes would have been too complex. Researchers then created a map of city census tracts according to ease of access to providers.

"Low-access" areas were defined as five or more contiguous census tracts with the highest ratios of adults per primary-care provider.

Nearly one-third of the city's low-access areas were neighborhoods whose populations were at least 80 percent African American. Put another way, the researchers wrote, "the odds of being in a low-access area were 28 times greater for census tracts with a high proportion of African Americans than in tracts with a low proportion of African Americans."

Race appeared to be a far more significant factor than insurance or income.

"Philadelphia as a whole is not lacking in total number of primary-care providers," said Elizabeth Brown, the paper's first author, who is a physician at Christiana Care in Newark, Del., but collected much of the data while a Robert Wood Johnson scholar at the University of Pennsylvania's Leonard Davis Institute of Health Economics.

The team found a citywide ratio of 1,073 adults per primary-care provider, many of whom may be affiliated with - and situated near - major academic medical centers. But individual census tracts varied by a factor of 10 either way.

Racial disparities in access to primary care have been found elsewhere around the country but usually at the county and state level. Brown said this was the first research to compare census tracts.

Nevertheless, there is a lot that the study was unable to examine.

The "patient experience," Brown noted, is not just about geography but includes time in the waiting room, difficulty of getting doctors on the phone, and other factors. The study was unable to consider how health care is used - how far, for example, patients are willing to travel. Nor does it explain why providers have chosen certain locations.

Although the differences according to health coverage that were found in the study were not dramatic, physicians generally "tend to go where people are insured," said Thomas Farley, commissioner of the Philadelphia Department of Public Health. "Community health centers fill in some of the gaps, but they don't fully make up for those market-driven forces."

Farley said that the new data, which are more "fine-grained" than what was available to policymakers in the past, would be "useful to the extent that we can plan and try to direct resources into these areas."

The study identified six groupings of census tracts with low access to primary-care providers. They do not follow commonly used neighborhood boundaries, but roughly include: parts of North and South Torresdale; pieces of East and West Oak Lane, Ogontz, and a section of East Mount Airy; parts of West Philadelphia centered on Haddlington and Overbrook; sections of Southwest Philadelphia's Eastwick and Elmwood on the west side of the Schuylkill; parts of Grays Ferry, Passyunk, Schuylkill, and Point Breeze on east side of the river; and pieces of Oxford Circle, Lawndale, Crescentville, Frankford, Wissinoming, and Holmesdale.

All but the last are situated near the edges of the city, rather than in central areas, and they tend to be "areas where there has been a [comparatively recent] demographic shift" that also brought greater poverty, said Suzanne Cohen, an administrator at the Health Federation of Philadelphia, a network of community health centers in Southeastern Pennsylvania.

"There are these neighborhoods in the Northeast and parts of the Northwest that may have once been mainly white working-class populations and now are areas of color," with higher poverty levels, said Natalie Levkovich, the organization's executive director.

It can take years to fund and build new health centers, and most existing clinics opened long ago.

"There is a lot of health care around here but it is not necessarily planned or implemented in ways that are most responsive to needs," Cohen said.