Revisiting Physician Distribution by Concentration Coding

Geographic coding often involves concentrations of people relative to land area such as rural or urban or most urban. Why do studies of physician workforce use coding based on ratios of people to land area? Why not use ratios of health workforce or physician concentrations as compared to people?
Top concentrations, marginal concentrations, and underserved concentrations are more relevant to those seeking care, and are most relevant for basic health access where local or adjacent zip code care is a priority.
Also using workforce concentrations, types of workforce can be compared. One important area stands out. The MD, DO, NP, and PA family practice employed component is the only component that distributes according to the population and therefore according to primary care demand. All other primary care, specialty, hospital based, and subspecialty choices are more likely to be found in zip codes with increasing concentrations of physicians. Claims of better or best distribution are only about family practice and only when graduates stay in family practice.
What matters with regard to physician workforce is the ratio of physicians to the population. Patterns of workforce concentration can also be compared to various populations. Top concentrations create their own consequences, as in doughnuts of zip codes with shortages of workforce that surround clusters of top concentration zip codes. This is a design that results in the most barriers to health access. Primary care is also concentrated inside of concentrations, with the exception of family practice.
Physician Distribution by Concentration Coding emerged from immersion research involving secondary physician databases. With physicians in 2005 compiled by zip code, patterns of concentration were more easily understood.
Top concentrations tend to be subspecialty, academic, and hospital in focus with a vertical orientation of the design.
Most Americans are found in zip codes that are horizontal or health access in focus, dominated by primary care and generalists and general types of specialties.
This presents a problem because the workforce most needed by most Americans is the workforce least produced and least retained by American designs.
What emerges is the fact that those influencing health professional training and multiple Congresses and Presidents over many decades are found in top concentrations with benefits bent steadily this direction with little real competition. The health care delivery most promoted as outstanding to the world arises from these zip codes. The fact is that the United States has a Super Center design with a super sized consumption of health care spending and health care workforce and health care consequences – including lesser health and wealth for substantial portions of the United States population. More details and category characteristics can be found at Physician Distribution by Concentration.
Concentration Coding Categories

Physicians per 100,000 Population (280 is avg)
% of Office Based Economic Impact /
 % of US Physicians
% of Total US Pop /
% of FM Docs
Physician to Pop and FM to Pop Ratio
Super Center 200 or more physicians, < 1% land area
11 - 12%
20% of FM
4 to 1
1.8 to 1
Major Center 75 to 199 docs,  3% land area
27% of FM
1 to 1
1 to 1.2
Marginal Urban higher income and lowest poverty
25% of FM
1 to 2
1 to 1.25
Urban Underserved lower income and higher poverty
7% of FM
1 to 3
1 to 1.5
Marginal Rural average income and average poverty
8 - 9%
10% of FM
1 to 2
1 to 1
Rural Underserved lower income and higher poverty
8 - 9%
9% of FM
1 to 3
1 to 1

Highest poverty urban or rural sites have about 60 physicians per 100,000. AMA Economic Impact of Office Based Physicians used with AMA Masterfile 2005
Graphics of the PDC Coding

Inside of concentrations = Super Center and Major Center zip codes with one-third of the population and highest concentrations of physicians, health workforce, economics, income, facilities, health spending, and economic impact from health care. Zip codes inside of concentrations are also clustered together in small portions of states, counties, and cities for least accessible health care. Inside of concentrations are even higher concentrations of health spending and economic impact per capita.
Outside of concentrations = Marginal or Underserved zip codes with two-thirds of the population and same or greater proportions of elderly, poor, near poor, rural, underserved, disadvantaged, and complex populations as well as lower health resources and health spending.
Two geographic patterns are common with lesser concentrations. These include large areas of low concentrations and doughnut patterns. Doughnut rings of lower to lowest workforce concentration surround zip codes with highest concentrations of workforce. Doughnuts can be urban or rural. New York City urban zip codes surrounding Manhattan indicate highest central and lowest peripheral concentrations. In the Midwest highest metro concentrations are surrounded by nearby rural zip codes, at least until urban sprawl overtakes low concentrations.
The most subspecialized workforce is found at 60 – 65% inside of Super Center zip codes in 1% of the land area with 11% of the population. About 80 – 92% are found inside either Super Center or Major Center concentrations along with 85% or more of residents in training, faculty, and research physicians. Training dollars and research dollars follow these concentrations of workforce as do concentrations of health spending for the most specialized procedures.
Designs developed over the past 100 years have consistently favored those most inside of concentrations. Zip codes inside of concentrations can access all lines of health service revenue and reap the highest levels of revenue in each line. Zip codes inside can recruit staff, nursing, clerical, and practitioner workforce away from primary care and from lesser concentrations due to greater health spending – by design.
Primary care is assured the least experienced personnel and workforce by designs that send the most experienced inside of concentrations leaving those most inexperienced and those most dedicated behind on the front lines. New designs by states and insurance companies may result in even less primary care spending sending even more workforce away from basic health access to top concentrations – or the US could continue the old design of too little revenue for the increasing cost of delivering primary care for steady, albeit slower declines.  


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