About

Cyrus M Kosar is an Assistant Professor of Health Services, Policy and Practice at Brown University. He is a health services researcher and health economist whose research broadly pertains to the delivery of care in the Medicare Program. His specific areas of focus include post-acute care, long-term care, end-of-life care, rural health care, risk-adjustment, Medicare Advantage, extreme weather events and Medicare spending, and scope of practice reform. He is currently the principal investigator of a National Institute on Aging-funded R01 that aims to provide evidence on the impact of various post-acute and long-term care policies. His background includes a PhD from Brown University obtained in 2021, a Master's degree from Boston University in 2010, and a Bachelor's degree from Boston University in 2009.

Research topics

• Medicine
• Internal medicine
• Gerontology
• Nursing
• Emergency medicine
• Immunology
• Demography
• Virology
• Environmental health
• Pediatrics

Selected publications

• Data documentation for State Medicaid Programs Face Increased Spending On Medicare Premiums

  Brown Digital Repository · 2026-04-28

  datasetOpen access
  PublisherDOI

• Changes in Inpatient and Skilled Nursing Facility Care After the Medicare 3-Day Rule Reinstatement

  JAMA Internal Medicine · 2026-02-09

  articleOpen accessSenior author

  Importance: On May 12, 2023, the Medicare program reinstated the long-standing 3-day hospitalization rule for skilled nursing facility (SNF) care after it had been waived for more than 2 years during the COVID-19 pandemic. This abrupt policy change offers a natural opportunity to assess the contemporary impact of the rule on inpatient and postacute care. Objective: To evaluate changes in inpatient length of stay, SNF utilization, spending, and short-term health outcomes among traditional Medicare beneficiaries following reinstatement of the 3-day hospitalization requirement. Design, Setting, and Participants: This retrospective cohort study of traditional Medicare beneficiaries with acute care hospitalizations included data from January and November 2023. A regression discontinuity design was used to examine changes in outcomes after the 3-day rule's reinstatement. Data were analyzed from June to November 2025. Exposures: Hospitalizations before vs on or after May 12, 2023. Main Outcomes and Measures: Primary outcomes were hospitalization for at least 3 days and SNF discharge. Secondary outcomes included 30-day rehospitalization, 30-day mortality, Medicare spending, and total SNF days. Results: This study included 332 044 unexposed hospitalizations (178 547 female patients [53.8%]; mean [SD] age, 78.3 [8.3] years) and 338 375 exposed hospitalizations (182 049 female patients [53.8%]; mean [SD] age, 78.2 [8.3] years) for traditional Medicare beneficiaries in 2023. Reinstatement of the 3-day rule was associated with a 1.13 percentage point (95% CI, 0.61-1.66; P < .001; relative change, 1.9%) increase in the likelihood of an inpatient stay lasting at least 3 days. Among patients discharged to SNFs, 3-day rule reinstatement increased the probability of an at least 3-day hospitalization by 5.57 percentage points (95% CI, 4.91-6.24; P < .001; relative change, 6.4%). No significant changes were observed in the overall probability of SNF discharge, 30-day rehospitalization, 30-day mortality, Medicare spending, or total SNF days. Subgroup analyses showed greater increases in at least 3-day stays among patients hospitalized for hip fractures and patients with dementia. Conclusions and Relevance: In this cohort study, reinstating Medicare's 3-day hospitalization requirement was associated with longer inpatient stays without decreases in SNF utilization or improvements in short-term health outcomes. These findings suggest that the policy imposes additional costs on hospitals while failing to lower Medicare spending on hospitalized patients. More generally, results raise questions regarding the value and continued relevance of a broadly applicable 3-day inpatient stay rule in the traditional Medicare program.

  PublisherOA PDFDOI

• Association of Medicare Advantage Enrollment Growth and Changes in Home Health Supply, 2011–2022

  Journal of the American Geriatrics Society · 2026-01-19

  articleOpen access

  Medicare Advantage (MA) enrollment has grown rapidly over the last two decades. MA insurers have a strong incentive to reduce their health care spending because they are paid on a risk-adjusted per capita basis. One area they have targeted in reducing health expenditures has been home health [1-4]. MA plans have a number of tools to try to reduce home health care use, including the use of prior authorization, restrictive networks, and cost-sharing [1]. MA plans also have flexibility in the prices that they pay HHAs and may reimburse at lower levels than the administratively set prices in traditional Medicare (TM) [5]. In recent years, the number of home health agencies has declined substantially while MA enrollment has grown rapidly [5]. We investigated whether rising MA enrollment is related to declining home health supply. Our objective was to examine the association between county-level changes in MA penetration and county-level changes in home health supply and use from 2011 to 2022. We calculated the number of home health agencies serving each county in 2011 and 2022 using the Outcome and Assessment Information Set (OASIS) linked to beneficiary county from the Medicare Master Beneficiary Summary File (MBSF). OASIS contains assessments that must be completed by all Medicare-certified HHAs and includes all Medicare patients, regardless of whether they are enrolled in MA or TM. In addition to home health supply, we calculated three measures of home health use: the number of starts of care, the number of post-acute starts of care, and the number of community-initiated starts of care. We expressed all values per 1000 Medicare beneficiaries. We also used publicly available data on county MA penetration, changes in economic factors, and urbanicity. More details on measures and the sample can be found in the Supplement. For each county, we calculated the change in the MA penetration and the number of home health agencies per 1000 beneficiaries by subtracting the 2011 value from the 2022 value. We used a binned scatter plot to visually characterize this relationship. We also used ordinary least squares regressions of the change in home health supply and change in home health use on the change in MA penetration, adjusting for changes in the share of people in poverty, the median income, and the unemployment rate as well as the county's urbanicity as measured by its Rural Urban Continuum Code. Counties with greater growth in MA penetration had larger declines in the number of HHAs per 1000 beneficiaries (Figure 1). Adjusting for other factors, a 10-percentage point larger increase in MA penetration was associated with 0.54 (95% CI: −0.65, −0.42) fewer HHAs per 1000 beneficiaries, an 11.5% decline relative to the baseline mean (Table 1). A 10-percentage point larger increase in MA penetration was associated with 6.08 (95% CI: −9.20, −2.95) fewer starts of care per 1000 beneficiaries and 5.53 (95% CI: −0.810, −0.296) fewer community-admitted starts of care, declines of 5.7% and 13.7% relative to the baseline means. However, there was no statistically significant relationship between changes in MA penetration and changes in the use of post-acute care home health. In this study, we found that US counties with greater growth in MA enrollment had greater declines in home health supply and use. Our study was limited by the fact that there may be unobservable variables related to both changing MA penetration and home health supply and by the fact that changes in the number of home health agencies is an imperfect measure of access to care, for example because agencies are different sizes. As MA continues to grow, it may reshape the home health industry and beneficiary access to home health care. Concept and design (J.M., D.J.M.); statistical analysis (J.M., J.S.); data interpretation (all authors); drafting manuscript (J.M.); review of manuscript (all authors). This research was supported by the National Institute on Aging (5P01AG027296). Drs. Kosar and Rahman also received funding from the National Institute on Aging (1R01AG089051-01). This work was supported by the National Institute on Aging, 1R01AG089051-01, 5P01AG027296. The authors declare no conflicts of interest. Data S1: Supporting Information. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

  PublisherOA PDFDOI

• The Pace of Cognitive Aging in Older Adults Without a Neurocognitive Disorder

  Innovation in Aging · 2025-12-01

  articleOpen access

  Abstract The pace of cognitive change without a neurocognitive disorder is one of the major questions in cognitive aging. The Children of the Depression Age (CODA) cohort of the Health and Retirement Study (HRS) is ideal for studying cognitive aging because it has a long follow-up (22 years) and a narrow age range at baseline (67-74 years). We analyzed data on delayed word recall performance in HRS-CODA (N = 2,295), gathered every other year during the follow-up period. Using latent growth curve modeling and treating delayed recall as a categorical outcome, we found a quadratic model showed better fit to the data than a linear model, with no strong evidence for a practice and retest effect. When calculating the pace of normative aging, our results suggested normative (defined as the absence of a dementia diagnosis over the follow-up period) memory decline is about -0.05 standard deviations per year (SD/y), but is better characterized by age specific estimates of -0.04 SD/y, -0.10 SD/y, and -0.15 SD/y for individuals in their 70s, 80s, and 90s, respectively. These results would suggest that memory decline, in the absence of a recognized dementia and without a confounding of baseline age differences and longitudinal age changes, would be present but almost imperceptible to an individual in their eighth decade, but noticeable in their ninth and quite impairing in their tenth decade.

  PublisherOA PDFDOI

• Is Managed Care Effective in Long-term Care Settings? Evidence from Medicare Institutional Special Needs Plans

  National Bureau of Economic Research · 2025-09-01 · 1 citations

  reportOpen accessSenior author

  Nursing homes face unique financial incentives that encourage under-investment in onsite clinical capabilities and overreliance on hospitals to triage and care for residents with dementia, contributing to high levels of health care spending for this population.A proposed solution to align incentives are Institutional Special Needs Plans (I-SNPs), which combine capitated financing with plan-provided onsite clinician presence.Using 12 million resident-quarters of data from 2016-2022, we exploit the timing of nursing homes' I-SNP contracting to instrument for plan enrollment and estimate causal effects on hospitalization and other health outcomes.We found that I-SNP enrollment reduced quarterly hospitalization rates by 3 to 4 percentage points, which equates to one third of hospitalizations relative to the sample mean.We do not find consistent evidence of an impact on other health outcomes and quality of care indicators.

  PublisherDOI

• Greater Physician Supply Associated with Lower Mortality in Rural Counties: A 23-Year County-Level Longitudinal Observational Study

  INQUIRY The Journal of Health Care Organization Provision and Financing · 2025-09-01

  articleOpen access

  Rural U.S. residents face higher mortality rates and reduced access to primary care physicians. Prior studies report mixed findings on physician supply and health outcomes, and few have examined whether increasing supply reduces rural-urban mortality disparities. The objective was to quantify the marginal benefits of additional primary care physician supply in rural and urban areas, independent of other healthcare and socioeconomic factors. We conducted a 23-year county-level longitudinal observational study of 2942 U.S. counties (1992-2014). Mortality rates were obtained from CDC WONDER, physician supply and socioeconomic characteristics from the Area Health Resource File, and rural-urban classification from the USDA's 2013 Rural-Urban Continuum Codes. We estimated regressions of age-adjusted mortality rates as a function of physician supply, rurality, and county-level characteristics. Despite the higher per-capita supply of hospital beds and post-acute care services in rural areas, physician supply was lower and grow more slowly than in urban areas. County-level analysis showed a negative association between physician supply and mortality. In rural counties, greater physician supply was associated with lower mortality rate; an increase of 1 physician was associated with 1.4 (CI: -1.963 to -0.836) and 0.936 (CI: -1.411 to -0.462) fewer deaths per 100 k population of older adults in rural counties adjacent and non-adjacent respectively, compared to 0.038 fewer deaths per 100 k population of older adults in urban areas. The declining physicians supply in areas where the number of physicians is already low is an alarming problem for rural communities. Efforts by policymakers to broaden rural health networks and increase rural medical personnel may be needed to address disparities in access to care and associated mortality outcomes. Although the dataset covers 1992 to 2014, the findings remain highly relevant given the continued rural physician shortages and widening mortality disparities that persist across the United States.

  PublisherDOI

• The Pace of Memory Decline in Older Adults without a Neurocognitive Disorder: Results from 22 Years of Follow-Up in a Nationally Representative Sample

  Neuroepidemiology · 2025-09-04 · 1 citations

  articleOpen access

  INTRODUCTION: The pace of cognitive change is one of the major questions in cognitive aging. The Children of the Depression Age (CODA) cohort of the Health and Retirement Study (HRS) is uniquely suited to study cognitive aging because it has a long follow-up (22 years) and a narrow age range at baseline (67-74 years) and presents a unique opportunity to study this topic. METHODS: We examined delayed recall data over the 22 years of follow-up in a nationally representative sample of the USA (HRS-CODA; N = 2,295 at baseline and N = 263 at the final follow-up wave), examining results for the entire sample and omitting participants with self-reported dementia. Data were analyzed using latent growth curve models, adjusting for baseline age, sex, years of education, and race/ethnicity. RESULTS: Respondents were predominantly female (62%), white (86%), and 71 years old on average at baseline. Our results suggest the pace of normative (defined as the absence of a dementia diagnosis over the follow-up period) memory decline is about -0.05 standard deviations per year (SD/y) but is better characterized by age-specific estimates of -0.04 SD/y, -0.10 SD/y, and -0.15 SD/y for an individual who was 75, 85, and 95, respectively. DISCUSSION: Memory decline, in the absence of a recognized dementia and without a confounding of baseline age differences and longitudinal age changes, would be present but almost imperceptible to an individual in their eighth decade, but noticeable in their ninth and quite impairing in their tenth decade. Future research is needed to examine other cognitive domains and with more robust measures.

  PublisherOA PDFDOI

• Trends in Long‐Term Care Ombudsman Program Funding and Its Relationship to Nursing Home Resident Care

  Milbank Quarterly · 2025-10-24

  articleOpen access

  Policy Points Funding that states' Long-Term Care Ombudsman Programs (LTCOPs) receive must cover all activities in that state related to the care of all individuals in nursing homes (NHs) and board and care (i.e., residential care communities, assisted living, and similar care homes); over time, duties and demands have expanded without similar increases in funding. States are contributing more to their federally mandated LTCOPs than they have historically. Evidence from this study suggests that increased spending on LTCOPs is associated with improved NH resident care, supporting the National Academies of Sciences, Engineering, and Medicine's recent call for increased funding to LTCOPs. CONTEXT: Funded partially by the Older Americans Act, state Long-Term Care Ombudsman Programs (LTCOPs) provide a critical role in serving as advocates for older adults in long-term care (LTC) facilities. Ombudsmen regularly visit residents, resolve disputes, and assist with discharge planning. In 2022, the National Academies of Sciences, Engineering, and Medicine called for increased LTCOP funding to improve nursing home (NH) quality. However, it is unclear how changes in program funding are associated with the care provided to NH residents. Based on the functions that the LTC Ombudsmen are intended to provide, we hypothesized that increases in LTCOP spending would be associated with improved care in NHs. METHODS: We examined 20-year trends in funding for the LTCOP (2000 to 2019). Using 2011-2019 data from the National Ombudsman Reporting System, LTCFocus.org, Centers for Medicare & Medicaid Services Care Compare, and the Area Health Resource File, we examined the relationship between LTCOP spending per LTC bed at the state level and NH outcomes, controlling for year, state, facility, and market characteristics. FINDINGS: Overall, LTCOP funding increased over 20 years. However, the share of federal contributions to the LTCOP has decreased from 58.8% in 2000 to 46.9% of the total program's budget in 2019. The LTCOP spent an average of $37.30 per LTC bed in 2019, with wide state variation. In 2011, the average share of residents receiving antipsychotics was 25.4%, the share of those who were physically restrained was 2.9%, and the share of those with low-care needs was 13.5%. For every $100 annual increase in total spending per bed, there was a statistically significant 1.32, 1.13, and 2.95 percentage-point decrease in the share of residents receiving antipsychotics, those who were physically restrained, and those who with low-care needs, respectively. CONCLUSIONS: States that have increased funding for their LTCOP observe better NH resident care. These findings support calls to increase funding for LTCOPs.

  PublisherOA PDFDOI

• Corrigendum to “Level of consciousness at discharge and associations with outcome after ischemic stroke” [Journal of the Neurological Sciences, Volume 390 (2018): 102–107]

  Journal of the Neurological Sciences · 2025-11-20

  articleOpen access
  PublisherOA PDFDOI

• Effects of Medicare Advantage Growth in Nursing Homes on Care Quality and Resident Outcomes: Using Shift-Share IV

  Innovation in Aging · 2025-12-01

  articleOpen access

  Abstract Medicare Advantage (MA) now covers 54% of all Medicare beneficiaries. MA growth has expanded to nursing home (NH) setting, covering 37% of short-stay patients and 32% of long-stay residents in 2021. The impact of MA growth in NHs remains understudied. Using a shift-share instrumental variable (SSIV), we estimated effects of MA growth in NHs on care quality. We identified MA enrollment of Medicare-enrolled NH residents using the Medicare enrollment file (2015-2019). NH quality measures included CMS five-star overall and staffing ratings and health deficiencies. Population-specific outcomes, derived from claims, included proportion of short-stay residents with 30-day rehospitalization and death, and the quarterly rate of hospitalization and death among long-stay residents. The main explanatory variable was high MA share in NHs (top quartile NH MA share annually). We used a SSIV, leveraging an exogenous shift—the annual national MA contract growth—linked to baseline NH contract share. We estimated a two-stage least squares (2SLS) regression with NH and year fixed effects, adjusting for NH and county characteristics and clustering standard errors for NHs. Among 18,711 NHs (83,215 observations over five years), 31% had high MA share. The first-stage F-statistic was 528.7 (Coef. 0.12, P &amp;lt; 0.001), confirming IV strength. In 2SLS results, high MA share in NHs was associated with a 0.6 increase in staffing ratings (95% CI 0.4-0.9; P &amp;lt; 0.001), an 18.8% relative increase, but not with overall star-rating, deficiencies, or population-specific outcomes. Although these results suggest MA growth has improved staffing levels at NH, the mechanisms underlying these findings warrant further investigation.

  PublisherOA PDFDOI

Frequent coauthors

• Vincent Mor

  Providence College

  89 shared

• Momotazur Rahman

  Brown University

  64 shared

• Sharon K. Inouye

  Beth Israel Deaconess Medical Center

  55 shared

• Richard N. Jones

  Butler Hospital

  53 shared

• Edward R. Marcantonio

  Harvard University

  48 shared

• Kali S. Thomas

  Johns Hopkins University

  48 shared

• Elizabeth M. White

  47 shared

• Thomas G. Travison

  Hebrew SeniorLife

  32 shared

Labs

• Kosar, CyrusPI

Education

• Ph.D.

  Brown University

  2021

• M.A.

  Boston University

  2010

• B.A.

  Boston University

  2009