Table 2.

Key references related to the impact of cost-sharing on utilization and total spending in low-income populations.

AUTHOR(S)	POPULATION	METHODS	MAJOR FINDINGS
Chernew et al., 2008	42,845 adults with employer-sponsored health insurance with diabetes or heart failure from 2002–2004	Used data from MarketScan Commercial Claims database. Medication adherence examined using regression model controlling for multiple demographic characteristics and area-level proxy for household income	Increased copayments decreased adherence for almost all medication classes among those in the lowest income group (<$30,000/year), but much less so in all other income groups
Cunningham, 2002	39,000 American adults age 18–64, including about 1,800 with Medicaid or state coverage	Using the Community Tracking Survey in 2000–01, a nationally representative telephone survey, compared perception of participants’ ability to obtain prescription drugs due to cost based on insurance status	26% of adults with Medicaid/state coverage and 29% of uninsured adults were unable to obtain a prescription drug due to cost in the past year, compared to 8% of those with employer-sponsored insurance For those with 2 or more chronic medical conditions (e.g., diabetes, hypertension), this rose to 41% for those with Medicaid/state coverage and 61% uninsured, compared to 15% with employer-sponsored insurance
Cunningham, 2005	About 1,600 American adults aged 18+ enrolled in Medicaid	Data from Community Tracking Survey in 2000–01 and 2003 as well as state surveys regarding prescription drug policies in 2000 and 2003. Regression models examined effects of five state policies regarding prescription drugs (use of prior authorization, copayments, dispensing limitations, generic drugs, and step therapy) on respondents’ perception of ability to obtain prescription drugs.	More than 1/5 unable to get prescription drugs due to cost; this is higher than other populations even when adjusted for income and chronic health status Participants in states with more of these policies about 10% more likely to report access problem due to cost When evaluated independently, copayments had no significant effects on access.
Domino et al., 2011	North Carolina Medicaid beneficiaries age 19–64 who experienced a $2 prescription medication copay increase and reduction in days supply of meds in 2001.	Difference-in-differences design comparing adherence changes in those with North Carolina Medicaid (which implemented a copayment increase and days-supply limitation) with Georgia. Analysis using CMS claims data.	General decrease in adherence, with observed decreases larger in days allowed supply changes than in copayment increases only Lower adherence did not increase hospitalizations Overall Medicaid program spending declined but was attributed more to limiting days supply than copay increase
Farley, 2010	Mississippi Medicaid beneficiaries with schizophrenia who experienced $2 prescription medication copayment increase among other changes in 2002	Difference-in-differences design comparing adherence changes in those with Mississippi Medicaid (which implemented a copayment increase) with Indiana and Minnesota which did not. Analysis using CMS claims data.	Patients significantly reduced their antipsychotic compliance Slight reduction in outpatient mental health visits No evidence of increased emergency department visits or hospitalizations
Guy, 2010	Low-income childless adults age 19–64	Difference-in-differences design using 1997–2007 data from the Behavioral Risk Factor Surveillance System, a nationally representative telephone survey. Study modeled changes in preventive care after insurance expansions with and without copayments.	Insurance coverage improved regardless of cost-sharing requirements when public insurance was expanded to childless adults Beneficiaries of programs with small (less than $3/service) cost-sharing requirements had improved screening rates, while those enrolled in programs with increased cost-sharing requirements ($5–$25) did not
Hartung et al., 2008	Oregon Medicaid beneficiaries who experienced new copayments in 2003, average age about 38 years old.	Interrupted time series analysis using aggregated Oregon Medicaid Fee-For-Service data focusing on a range of prescription drug and service use outcomes for three years after institution of copayments	Utilization of all prescription drugs decreased by 17% There was significantly decreased utilization for each therapeutic category to different extents No changes observed in outpatient service utilization
Lowe et al., 2010	Oregon Medicaid beneficiaries age 18–64 who experienced increased cost-sharing in 2003, including $50 emergency department copayments.	Difference-in-differences design compared those who experienced increased cost-sharing (OHP Standard plan) with those who did not (OHP Plus plan) using state Medicaid claims data.	In the OHP Standard plan, adjusted rates of ED use fell 16% after cutbacks and rose 9% after partial restoration of benefits; in the OHP Plus plan, these rates rose over the same time periods ED use among OHP Standard enrollees fell 18% compared with OHP Plus enrollees When considering presumably more serious visits that resulted in hospitalization, OHP Standard enrollees had a 24% decrease
Mortensen, 2010	Adult Medicaid beneficiaries age 19–64 in multiple states	Difference-in-differences design comparing utilization in states who underwent copayment increases with those who did not. Used data from the Medical Expenditure Panel Survey (MEPS) from 2001–06, a nationally representative survey. Indicators are included for implementation of Medicaid copayment policy.	No evidence that those beneficiaries living in states which implemented a copayment increase decreased their non-emergent emergency department visits
Subramanian, 2011	10,241 adult Medicaid beneficiaries age 21–64 with cancer in Georgia, Texas, and South Carolina	Difference-in-differences design compared one state whose Medicaid beneficiaries experienced increased cost-sharing (Georgia) with those who did not experience increases to the same extent (Texas and South Carolina) using state Medicaid claims data linked to cancer registry data from 1999–2004	After implementation of copayment in Georgia, number of prescription days (number of prescriptions multiplied by days supply) decreased 17% while control states’ prescription days increased Probability of ED visit increased in Georgia only Patients with multiple comorbidities in Georgia decreased their prescription use the most Total Medicaid cost increased in all states, but increased the most in Georgia
Von Korff et al., 2008	14,515 adults over 21 years old with family incomes up to 200% of FPL from western Washington state who were members of Basic Health Plan (BHP), which underwent increased cost sharing in 2004.	Difference-in-differences design compared individuals’ out-of-pocket health costs due to increased cost-sharing in Washington’s Basic Health Plan with age-sex-residence matched controls not enrolled in Medicaid or BHP.	Enrollees experienced a 100% increase in out of pocket costs over 2 years, compared with approximately 40% in non-BHP, non-Medicaid controls No increase in disenrollment with increased cost-sharing
Wallace et al., 2008	10,381 adult Oregon Medicaid beneficiaries age 18–64 with incomes <100% FPL who experienced increased cost-sharing in 2003	Difference-in-differences design compared program expenditures and service use of those Medicaid beneficiaries who experienced program changes including increased cost sharing with those who did not.	Expenditures for pharmacy services, ambulatory services, and ED use decreased significantly Expenditures for inpatient and hospital-based services increased significantly Total expenditures per person unchanged