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Logo of nihpaAbout Author manuscriptsSubmit a manuscriptHHS Public Access; Author Manuscript; Accepted for publication in peer reviewed journal;
Med Care. Author manuscript; available in PMC 2013 October 1.
Published in final edited form as:
PMCID: PMC3444646

Primary Care and Behavioral Health Practice Size: The Challenge for Healthcare Reform



We investigated the size profile of US primary care and behavioral health physician practices since size may impact the ability to institute care management processes (CMPs) that can enhance care quality.


We utilized 2009 claims data from a nationwide commercial insurer to estimate practice size by linking providers via tax identification number. We determined the proportion of primary care physicians, psychiatrists, and behavioral health providers practicing in venues of >20 providers per practice (the lower bound for current CMP practice surveys).


Among primary care physicians (n= 350,350), only 2.1% of practices consisted of >20 providers. Among behavioral health practitioners (n=146,992) and psychiatrists (n=44,449), 1.3% and 1.0% of practices, respectively, had >20 providers. Sensitivity analysis excluding single-physician practices as “secondary” confirmed findings, with primary care and psychiatrist practices of >20 providers comprising, respectively, only 19.4% and 8.8% of practices (difference: p<0.0001). In secondary analyses, bipolar disorder was used as an tracer condition to estimate practice census for a high-complexity, high-cost behavioral health condition; only 1.3-18 patients per practice had claims for this condition.


The tax identification number method for estimating practice size has strengths and limitations that complement those of survey methods. The proportion of practices below the lower bound of prior CMP studies is substantial, and care models and policies will need to address the needs of such practices and their patients. Achieving a critical mass of patients for disorder-specific CMPs will require coordination across multiple small practices.


Practice Size, Care Management Processes, and Quality

Organized care management processes (CMPs)—the systematic use of guidelines supported by clinical information systems and care management—are the cornerstone of quality improvement in primary care and multi-specialty group practices1-3. They are a key component2 of patient-centered medical homese.g.,4,5 and accountable care organizations (ACOs)e.g.,6,7. CMPs require sufficient organizational resources to support their implementation, such as information technology, external incentives, practice ownership type, and ability to respond to external incentives1-3.

Additionally, CMP utilization1,3 and other indices of quality8,9 appear to depend at least in part on practice size. However, there are surprisingly few published, peer-reviewed studies of US physician practice size, and none of behavioral health practice size. The AMA Physician Marketplace Report for 200110 indicated that 37.3% of physicians practiced solo, while 21.9% practiced in groups of ≥10 physicians. By 2007-200811, the proportion of solo practitioners had decreased to 24.6%, but the proportion of groups of ≥10 providers actually dropped to 16.7%. Generally consistent with these findings, the 2006 National Ambulatory Medical Care Survey found that 32% of primary care physicians were in solo practice while only 7% practiced in groups of ≥1012. Data from the 2008 Health Tracking Physician Survey13,14 indicated that 32% of US physicians worked in 1- to 2-physician practices, 15% in practices of 3-5 physicians, 19% in practices of 6-50 physicians, and the remainder in a variety of larger organizations or hospital-based practice. The Practice Size Exploratory Project (PSEP)15 analyzed data from 10,220 Medicaid providers in 4,363 practices across four states. They found that in Arkansas, Michigan, and Pennsylvania 24-32% were in solo practice and 22-27% practiced in groups of ≥10. However, in urban New York 13-16% of Medicaid providers practiced solo, while 51-71% practiced in groups of ≥2015.

Behavioral Health Care: The Added Challenge

Mental disorders affect over 25% of the US population at any one time16. Affected individuals typically receive highly fragmented, suboptimal quality care17, and those with serious mental illness die 25 years earlier than the US average18. Within primary care, implementation of care management processes for depression lags behind that for common medical illnesses1,2. Further, while depressive and anxiety disorders are treated across general medical and behavioral health sectors, individuals with chronic disorders (including chronic or recurrent depressive and anxiety disorders) are typically treated in the behavioral health rather than general medical sector (48.3% vs. 12.7%, respectively)19. Coordinating care and improving quality for this population may also be enhanced via CMPs and related medical home methodologies20-22—but only if practice resources are adequate to support such processes.

Commercially Insured Care, Claims Data, and Practice Size

Even prior to healthcare parity legislation, 71.7% of individuals with chronic mental illnesses were covered by commercial insurance or Medicare, including 56.0% of those with psychotic or bipolar disorder23. Thus a substantial responsibility for the care of these populations is borne by providers working with commercial insurers.

We report here what is to our knowledge the first description of practice size for clinicians, particularly physicians, who provide commercially insured primary or behavioral health care, utilizing records of a large US commercial insurer. There are two novel aspects to this study. First, we focused on practices providing commercially insured care because the diversity of survey results indicates that sampling frame may affect practice size estimates. For example, most surveys10-14 show that one-quarter to one-third of physicians practice solo and 7-21.9% practice in groups of ≥10; however, sampling Medicare providers resulted in a more heterogeneous distribution, and resulted in estimating larger practice sizes15. In complementary fashion we therefore focused on physicians and practices providing commercially insured care, considering that this population might be characterized by smaller practice size than surveys indicate. Second, we estimated practice size not by survey but by linking tax identification numbers of claims as described in Methods. We reasoned that survey responses could under-represent small or solo practices which have fewer office staff to complete such surveys. We considered that this claims-based method would provide a complementary view of practice size, particularly in the commercially insured population, which we anticipated would be dominated by small practices.

We specifically hypothesized that the majority of primary care physicians, licensed behavioral health providers, and psychiatrists providing commercially insured care practice in venues with ≤20 providers, a threshold chosen because it is the lower bound of current CMP studies1-3. We further hypothesized that psychiatrist practice size would be even smaller than that for primary care physicians.

Additionally, we noted that CMPs are currently typically designed for specific conditions1-3,24,25, thus requiring a critical mass of qualifying patients for implementation and sustainability. We therefore investigated practice size and practice census for a specific chronic behavioral condition, bipolar disorder. This disorder was chosen as a tracer condition because it is the most expensive mental condition for US commercial insurers due to its severity and chronicity26, and among the most costly of all disorders to payers27, affecting over 9,000,000 Americans28, 44.1% of whom are covered by private insurance29. Additionally, the disorder provides an example of a DHHS-designated Multiple Chronic Conditions population30, as the disorder is by definition chronic31 and characterized by high rates of both psychiatric32 and medical33,34 chronic comorbidities. Managing quality for such populations will grow in importance as our population ages, since individuals with serious mental illnesses such as bipolar disorder consume an increasingly disproportionate share of both behavioral health and medical resources as they grow older35,36.


Aetna Inc. is the fifth largest provider of commercially insured behavioral healthcare in the US. They provide benefits through employers in all 50 states, with products and services targeted specifically to small, mid-sized and large multi-site national employers.

Using claims data, we identified participating and nonparticipating providers who filed an Aetna claim in 2009. We determined practice size based on number of providers linked to the same tax identification number submitted to Aetna. We used tax identification as a proxy for practice size, reasoning that individuals who billed together could be considered to function as a practice (see Discussion for limitations). We characterized primary care practice size based on the number of physicians (internists, family practitioners, pediatricians), and behavioral health practice size based on number of licensed behavioral health professionals (psychiatrists, psychologists, advanced practice nurses, social workers). We then specifically compared psychiatrist practice size distribution to that for primary care physicians using the median test, and investigated comparative proportion of practices with >20 physicians using the X2 statistic.

We next conducted a sensitivity analysis, repeating the analyses but excluding single-practitioner practices. This makes the very conservative assumption that all independent practice represents “secondary” activities (e.g., “moonlighting”), and that a provider's main clinical work is in a larger practice.

Finally, to characterize the practice settings in which care for bipolar disorder is provided, we constructed a practice size profile for psychiatrists who filed a claim in 2009 for treatment of bipolar disorder (ICD-9 codes 296.4-296.8, excluding 296.82, 296.89, 296.90, 296.99) and calculated average bipolar census (patients per practice) across the distribution.

Study Results

Among primary care physicians (n=350,350 Table 1A), 89.1% of practices were single-physician practices (48.6% of physicians), while 2.1% of practices included >20 physicians (35.2% of physicians) and 0.5% had >100 physicians (21.6% of physicians). Among licensed behavioral health providers (n=146,992; Table 1B) rates were, respectively, 94.7%, 1.3%, and <0.1% (75.3%, 13.6%, and 4.1% of behavioral health providers). Among psychiatrists (n=44,449; Table 1C), 89.3% of practices were single-psychiatrist practices, 1.0% of practices included >20 psychiatrists, and <0.1% of practices had >100 psychiatrists.

Table 1
Distribution of Behavioral Health Practices by Size: Number of Credentialed Primary Care Physicians (A), Behavioral Health Clinicians (B), Psychiatrists (C)a

Highly left-skewed distributions for both psychiatrists and primary care physicians did not result in significantly different medians (minimum, median, and quartiles = 1 for each group; maximum practice size for psychiatrists = 312, for primary care = 2,631; p=NS). However, fewer than half as many psychiatric practices as primary care practices consisted of >20 physicians (1.0% vs. 2.1%, X2(1)= 151.6; p<0.001).

Sensitivity analysis, considering all single-physician practices as “secondary” and excluding them, underscored primary results. Median practice size for both groups remained small, with psychiatrists practicing in significantly smaller practices than primary care physicians (median (quartiles), respectively = 3 (2-6) vs. 4 (2-8), p<0.001), and having fewer than half as many practices with >20 providers (8.8% vs. 19.4%; X2(1)=175.8, p<0.0001).

Among psychiatrists filing at least one claim in 2009 for bipolar disorder (n=6,757; Table 2A), a similar highly left-skewed distribution is seen, with single-psychiatrist practices comprising 93.2% of venues that cared for such patients, and 1.1% with >20 psychiatrists. From the perspective of the patient with bipolar disorder (n=26,652; Table 2B), 94.9% were seen in single-psychiatrist practices, while only 1.6% were seen in practices of >20 providers. The average bipolar census per practice was 1.3-18.0 bipolar patients per practice; excluding a single group of >100 psychiatrists that treated 18 bipolar patients, the range was 1.3-4.5.

Table 2A
Distribution of Providers Treating Individuals with Bipolar Disorder by Practice Size
Table 2B
Distribution of Patients with Bipolar Disorder by Practice Size


Commercially Insured Care in Practice Size Context

The vast majority of primary care and behavioral health practices utilizing commercial insurance consisted of ≤20 physicians, below the lower bound of practice size for current CMP implementation surveys1-3. As expected, this commercially insured primary care provider population revealed an even more left-skewed population than indicated by prior surveys. After excluding single-physician practices as “secondary,” the proportion of primary care practices with >20 physicians remained quite low (19.4%). However, including single-physician practices revealed a substantially larger proportion in single-physician primary care practices. Comparing physician-level data to surveys, 35.2% of primary care physicians practice in venues of ≥ 20 physicians, vs. 7%-21.9% in practices of ≥10 reported for most10-14 (though not all15) surveys. Further, 48.8% practice independently, vs. 24.6-32% reported in surveys10-15. It is possible that claims data over-report the proportion who practice independently (see next section). However, larger practice size among Medicaid providers15 compared to other surveys10-14 suggests that our findings, sampled through a commercial insurance frame, may also reflect a somewhat different—and not ignorable—population.

Of additional importance is that behavioral health providers practice in an even more left-skewed distribution than primary care physicians. These data, plus NSOP findings of lower rates of depression CMP adoption even in larger practices1,3, indicate a serious quality liability for this substantial16,19 population of Americans. Importantly, from the perspective of individuals with a specific chronic behavioral health condition that could be targeted by CMPs (using bipolar disorder as a tracer condition), the majority of commercially insured care appears to be delivered in very small venues (Table 2A) which each manage relatively small numbers of patients with that condition (Table 2B), thus making disorder-specific CMPs even more difficult to establish and maintain at the practice level. The number of patients with chronic behavioral health conditions like bipolar disorder managed solely outside of specialty behavioral health venues may be even smaller37, although this needs to be directly studied particularly in rural settings where specialty behavioral health care may be less available.

Limitations, Further Questions, and Future Directions

The use of tax identification numbers to link providers who practice together has strengths and limitations. The advantage compared to survey methodology is that providing these data takes no effort on the practice's part, while survey data requires that the provider or an office staff member submit the information. Survey methods thus risk under-representation of smaller practices or those with negligible infrastructure who may be less likely to return such surveys. Nonetheless, more detailed analyses using survey, interview, and qualitative methods are needed in order to accurately characterize care management processes in smaller practices. For instance, we cannot determine from our methodology whether additional clinical or non-clinical staff support the physicians or other behavioral health licensed providers that comprised the basis for our analyses. Contrarily, we also do not know the degree of integration that actually characterizes the day-to-day practice processes of providers who bill together. It is also important to understand the degree to which extra-practice resources support quality enhancement processes (e.g., insurer-based or practice association-based information management infrastructures or CMPs).

Additionally, we focused attention on an a priori practice size cutoff of >20 providers. Although this cutoff may seem arbitrary, it is based on the lower bound of prior large CMP survey populations1-3. We know from these surveys that even within among larger practices, smaller size is associated with lower rates of CMP utilization; we thus reasoned that even smaller practices size would represent even higher risk of non-utilization and unmet need in terms of CMP support—and therefore would need implementation strategies designed specifically around their needs.

Finally, the degree to which other commercially insured behavioral health populations with multiple, chronic conditions30 resemble bipolar disorder remains to be determined. Additionally it should be noted that the bipolar practice census figures reported here derive solely from Aetna-covered care and thus may represent only a proportion of a practice's total census of this condition. Nonetheless, even a tripling of these estimates yields a census so low that practice-based diagnosis-specific CMPs for this condition would be problematic to sustain.

Policy Implications

Two broad foci for policy initiatives can enhance the uptake of CMPs into smaller practice venues: policies can incent smaller practices to consolidate, and solo or small practices as they currently exist can be linked. The AMA surveys10-11 indicate some consolidation of solo practices between 2001 and 2007-2008; however, the proportion of practices with >10 providers actually shrunk. ACOs hold promise; however, to date they have been limited to integrations that include at least one large core organization38,39 rather than representing consolidation of multiple small practices alone. Thus smaller practices must become a policy and implementation focus.

There are several mechanisms by which existing small practices can be linked to implement and sustain CMPs. Independent practice associations (IPAs) have been associated with increased rates of CMP adoption, compared to non-associated medical groups of similar size3. Additionally, telehealth provides an avenue for CMP adaptation that can overcome the lack of critical mass of patients with a particular diagnosis in any single practicee.g.,40,41; however, reimbursement structures will have to align to support telehealth modalities42.

Powerful electronic linkages may derive from meaningful use of the electronic health record (EHR), although EHR use to date has been modest43. However, increasing EHR implementation has recently become a policy focus through the Health Information Technology for Economic and Clinical Health (HITECH) initiative of the 2009 American Recovery and Reinvestment Act. In one example of meaningful use of both the EHR and provider incentives in small practices44, a Center for Medicare and Medicaid Services demonstration project under the 2003 Medicare Prescription Drug, Improvement, and Modernization Act provided financial incentives to smaller practices to enhance preventive services and care for diabetes, congestive heart failure, and coronary artery disease. Initial report of over 500 practices with a mean size of 3.3 physicians indicated that 88% of participating practices earned the maximum incentive for which they were eligible, including 33% who utilized EHR.

Additionally, under the 2009 Affordable Care Act, state-level health insurance exchanges and commercial insurers can provide incentives or support for small practices. However, incentives themselves have had mixed effects, since traditional pay-for-performance models have yielded equivocal results even in larger organizationse.g.,45,46 even when bundled with care management strategies47.

More promising, state-level exchanges, commercial insurers, and related entities that can “bundle” smaller practices together, can support plan- or population-level CMP models. The DIAMOND initiative for depression in Minnesota indicates that partnership across health plans, providers, and the state can stimulate adaptation and implementation of evidence-base CMPs in under-resourced practices—although to date this initiative has involved primarily larger groups48. Further, the finding among larger practices that IPAs can enhance CMP implementation3 suggests that this approach is worth exploring for smaller practices as well.

Additionally, a recent study of implementation of the related patient-centered medical home (PCMH) framework among predominantly smaller practices49 indicates that such practices can establish up to 70% of PCMH criteria with or without formal external facilitation. Implementation was more difficult if multiple roles are affected, if coordination across units was necessary, if additional resources were needed, and if implementation changed an established care model. Thus some characteristics likely typical of smaller practices may actually make it easier to establish new processes (simpler systems, fewer work roles), while other characteristics predict more difficult transitions (need for additional resources,). However, definitive conclusions regarding the dependence of CMP implementation on practice size must await direct study. Notably in this regard, in this study patient perceptions of PCMH attributes actually decreased during implementation49, further underlining the need for direct, detailed study.

Thus in summary, the challenge of small primary care and behavioral health practices is a significant one, and one with which we will need to grapple for the foreseeable future. Present policy levers and clinical care models hold promise. What now is required is focused and sustained attention on smaller primary care and behavioral health practices among policymakers, providers, insurers, and health services researchers.

Funding Acknowledgements

This work was funded in part by NIMH grant R-01-MH079994 (AMK) as well as the VA Health Services Research and Development Center of Excellence, The Center for Organization, Leadership, & Management Research (COLMR) (MSB).


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