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CloudView blog

Ideas and insights to help health care providers stay informed and profitable in today's challenging health care environment.

ACAView:The ACA's Sustained Impact on Payer Mix in Medical Practices

by Iyue Sung, PhD, Director of athenaResearch

A range of research already shows that the Affordable Care Act (ACA) has reduced the rate of uninsured patients in the U.S. But relatively little has been published on how visit patterns have changed. To examine how the ACA is affecting community medicine the Robert Wood Johnson Foundation has been partnering with athenahealth on ACAView, an initiative to measure the impact of the ACA on medical practices. 

Our latest findings, based on data through March 2015, show the following changes to adult (18-64) visits to primary care providers (PCPs)*:

  • In relative terms, the proportion of visits to PCPs by uninsured patients has dropped substantially in Medicaid expansion states through the first quarter of 2015, with a smaller relative decline in non-expansion states: in expansion states, dropping from 4.6% in 2013 to 2.4% in 2015; in non-expansion states, from 7.2% in 2013 to 5.7% in 2015
  • The percentage of visits from patients with Medicaid coverage increased substantially in expansion states, from 15.6% in 2013 to 21.5% in 2015. In non-expansion states, visits from commercially insured patients increased moderately relative to the pre-ACA baseline, from 66.1% in 2013 to 68.1% in 2015. Medicaid visits in these states changed little, dropping slightly from 9.4% in 2013 to 8.9% in 2015
  • Early signs suggest that Medicaid beneficiaries in expansion states are starting to establish ongoing relationships with providers

Our research uses the athenahealth database, which continuously collects and maintains claims and electronic health record data from a national network of physicians and other health care providers, most of whom practice in community settings (non-academic, ambulatory practices). For this ACAView report, we have drawn on a cohort of 6,000 primary care providers who have been on the athenahealth network prior to 2011, across more than 6 million patient visits. These PCPs are a subset of the 16,000 providers on the athenahealth network prior to 2011, providing a robust representation of ambulatory practices in the U.S. This research brief is an update on the payer mix component of our recent comprehensive report.  


We have seen substantial shifts in payer mix, especially in states that have expanded Medicaid eligibility criteria. In expansion states, Medicaid visits, as a proportion of all visits, increased from 15.6% in the first quarter of 2013 to 21.5% in the first quarter of 2015 (Figure 1). As the share of Medicaid patients has increased, the proportion of visits by uninsured patients has fallen nearly by half, from 4.6% in 2013 to 2.4% in 2015.

In non-expansion states, the major change to the payer mix has been an increase in the percentage of commercially insured visits, which rose from a pre-ACA baseline of 66.1% to 68.1% in Q1 2015. Visits from uninsured patients also declined, from 7.2% at the baseline to 5.7% in 2015.

Payermix F1

Figure 2 provides additional detail on the timing of Medicaid payer mix changes in expansion states. After declining slightly in the fourth quarter of 2014, the Medicaid case mix hit a new high of 21.8% of visits in the first quarter of 2015. 

Payermix F2

While expansion states are seeing a sharp increase in Medicaid patients, in non-expansion states, the most notable change is an increase in the proportion of visits from patients with commercial insurance.

Figure 3 shows that commercial visits in non-expansion states dipped to annual lows in September 2013 and 2014 before climbing back up in the last quarter of both years (note the scale of the vertical axis magnifies the seasonal variation). A new high was reached in March 2015, presumably driven by enrollment of patients in subsidized health marketplace plans. 

Why did the commercial case mix increase in the fourth quarter of each of the last two years? We speculate that, as patients exhaust their deductibles later in the year, they attempt to address as many care needs as possible before the deductibles “reset” at the beginning of the next year. Other patients may be trying to exhaust their health savings account (HSA) balances before the end of the year.

Payermix F3

These changes in payer mix – an increase in Medicaid visits in expansion states and an increase in commercial visits in non-expansion states – are not surprising and reflect the states’ expansion policies. But will these changes be sustained? We think these changes will persist as long as current coverage expansions are maintained.

Figure 4 shows Medicaid case mix by patient tenure.   In terms of tenure, we categorize patients into three groups: 1) New patients are those with no visits to the practice for two calendar years before their first visit in a given year; 2) Second-year patients have had a visit within the calendar year prior to their visit in a given year; 3) Established patients have had at least one visit within the two calendar years preceding the first visit of a given calendar year.

As shown in Figure 4, new patients accounted for 18.3% of all adult Medicaid visits to PCPs in the first quarter of 2013 (pre-ACA), then shifting to 21.0% and 19.7% in 2014 and 2015 respectively.  In the first quarter of 2015, 20.1% of adult patient visits were from Medicaid patients that had just started seeing that same practice in the first year of the ACA, and have continued to receive care from the practice – this rate of second-year patients is at a higher proportion than before the ACA.

In other words, patients who were new in 2014 returned at a higher rate the subsequent year, compared to patients who were new in 2013. It thus appears that many of the Medicaid patients that first visited their practice during the first year of ACA-led coverage expansion continue to receive care from their new providers.

Payermix F4

In summary, the ACA has changed the payer mix for outpatient practices across the athenahealth network. Payer mix has shifted towards a greater share of Medicaid visits in expansion states, a greater share of commercial visits in non-expansion states, and a reduction in uninsured visits nationwide – though that reduction is far more substantial in expansion states.  

As the year progresses, we’ll dive deeper into other pockets of ambulatory settings, using various measures of utilization, reimbursement and health indicators.

You can learn more about our ACAView initiative at the ACAView section of either the athenahealth or RWJF websites. We welcome feedback and suggestions on the athenahealth Cloudview blog, or directly to, or @IyueSung and @JoshGray_HIT on Twitter.

athenaResearch associate Anna Zink contributed to this report.

*Please refer to the appendix of our most recent ACAVIew report for a comparison of our ACAView cohort of 16,000 providers vs the CDC’s National Ambulatory Medical Care Survey.

As a statistician, Iyue is responsible for methodology, analytic infrastructure, and extracting data-driven insights from the athenahealth patient database. 

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