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ACA 411: Data, Sources, Notes, and Definitions

To monitor the impact of the Affordable Care Act (ACA) in California, the California Health Care Foundation (CHCF) asked the State Health Access Data Assistance Center (SHADAC) to assemble data indicators that would provide policymakers and stakeholders with the means to readily track progress on the law's key objectives. This page provides a summary of the data sources and other pertinent details.

See below for:

Data File

The data file of all estimates used in the ACA 411 is available for users to create their own tables or visualizations. Data were last updated on 3/13/2017.

Sources and Notes

The majority of the data come from these sources:

  • California Health Interview Survey (CHIS). Note: Estimates exclude the population 65 years and over. CHIS data are weighted to California Department of Finance (DOF) population estimates. DOF estimates for CHIS 2013 were based on the 2010 Census. CHIS 2015-2016 doubled the fraction of interviews from cell phones to address the potential coverage error in random digit dial (RDD) telephone sampling that arises from an increasing fraction of the general population being accessible only by cell phone. In CHIS 2015, 9,727 adult interviews (46.2% of adult interviews) were conducted from the cell sample. In CHIS 2013-2014, 7,752 adult interviews were conducted from the cell phone sample (19.3%). Learn more about cell phone sampling from the American Association for Public Opinion Research. Get the public use data files.
  • CHCF/NORC's California Employer Health Benefits Survey. Performed by NORC at the University of Chicago for the California Health Care Foundation. Note: In 2005, this survey was conducted by CHCF and The Center for Studying Health System Change (HSC), a nonpartisan policy research organization located in Washington, DC, that merged with Mathematica Policy Research in 2013. See more information.
  • Covered California. California's health insurance marketplace. Learn more about it from Covered California and the California Health Benefit Exchange.
  • Kaiser/HRET's Employer Health Benefits Survey. By the Kaiser Family Foundation and the Health Research and Educational Trust. Learn more and get the public use data files.

Other data sources apply for these particular indicators:

  • Average Monthly Enrollment in State Public Programs: California Department of Health Care Services, Research and Analytic Studies Division (RASD), Medi-Cal Monthly Eligibles Trend Reports, and the ACA Expansion Adult ages 19-64. Learn more and get the reports.
  • Emergency Room Visits per 1,000 Population & Avoidable Emergency Room Visits as a Share of All Emergency Room Visits: SHADAC analysis of the California Office of Statewide Health Planning and Development (OSHPD) Emergency Department and Ambulatory Surgery Data. Learn how to access the data files.
  • Enrollment in Covered California by Subsidy Status and Metal Tier: Centers for Medicare & Medicaid Services (CMS), Effectuated Enrollment Snapshots. Get the data.
  • Families with Any ESI Offer & Families Offered ESI with All Family Members Enrolled: SHADAC analysis of National Health Interview Survey (NHIS) data, National Center for Health Statistics (NCHS). Note: The NHIS sample is drawn from the Integrated Health Interview Survey (IHIS), Minnesota Population Center, and SHADAC. Data were analyzed at the University of Minnesota's Census Research Data Center because state identifiers and continuous income were needed to produce the results, and these variables are restricted. Get the IHIS public use data files or learn how to access the restricted variables data files.
  • Families with High Health Care Cost Burden & Median Annual Out-of-Pocket Spending per Family: SHADAC analysis of the Current Population Survey's Annual Social and Economic Supplements (CPS SHADAC-enhanced). Get the public use data files.
  • Individual Market Purchasing Through Covered California: Enrollment reporting by the Centers for Medicare & Medicaid Services (CMS) (get the data) and Covered California (get the data).
  • Patients Using Safety-Net Clinics & Volume and Type of Services Provided by Safety-Net Clinics: SHADAC analysis of OSHPD Primary Care and Specialty Clinics Annual Utilization Data. Note: County and other local government clinics are not included in the data reported here. Get the public use data files.
  • Physicians Participating in Public Insurance Programs & Physicians Accepting New Patients: Voluntary supplement to the Medical Board of California License Renewal Survey. UCSF School of Medicine. The 2013 data cited are from the California Health Care Foundation report Physician Participation in Medi-Cal: Ready for the Enrollment Boom? (August 2014).
  • Potentially Preventable Hospitalizations as a Share of All Hospitalizations: SHADAC analysis of confidential OSHPD Patient Discharge Data. Learn how to access the data files.
  • Total Individual Enrollment & Total Small Group Enrollment: Enrollment reporting by the California Department of Managed Health Care (get the data files) and the California Department of Insurance (get the data files). Adjustments were made to reported enrollment numbers for Total Individual Enrollment to include deductible HMO enrollment. Combined reporting from these sources is available from the California Health Insurance Enrollment Database, available as a document download from CHCF.
  • Uncompensated Hospital Care: SHADAC analysis of OSHPD Hospital Annual Financial Data. Note: The data exclude Kaiser Foundation hospitals, which provide roughly 10% of general acute hospital care in California. Get the public use data files.


  • Any offer of employer-sponsored insurance means that at least one working nonelderly adult (age 18-64) is offered workplace insurance that could be used to cover other family members.
  • Avoidable emergency room visits are defined using the algorithm developed by the California Emergency Room Coalition, an advisory committee working on cost containment in the Medi-Cal program. See more information (PDF).
  • Cost-sharing subsidies, to reduce the costs of deductibles and other out-of-pocket expenses, may be available to people who meet certain income limits and purchase medical insurance through Covered California.

  • Effectuated coverage tracks the number of individuals who purchased health insurance through Covered California and had their coverage take effect after paying their first month's premium.

  • Family coverage refers to insurance that covers the worker and at least one dependent.
  • Family take-up means that all individuals eligible for employer-sponsored insurance (either as a worker or a dependent) are enrolled in that coverage. Analysis was limited to families with a nonelderly adult (age 18-64) head of household.
  • Family is defined as the health insurance unit, which includes one or more individuals in a household who would likely be considered a family unit in determining eligibility for private or public coverage.
  • Federal Poverty Guidelines (FPG) are issued by the US Department of Health and Human Services (HHS) each year and used to determine financial eligibility for certain federal programs.
  • Government premium assistance refers to premium subsidies, in the form of tax credits, that lower the monthly premium cost for people living at between 139% and 400% of the federal poverty guidelines (FPG).
  • Individual coverage is insurance purchased directly.
  • Individual premiums through the Covered California marketplace represent the monthly maximum that a 40-year-old individual will pay for silver plan health care coverage based on their income level.
  • NA indicates that data were not available.
  • Necessary care includes prescription and medical care.
  • NS indicates that data did not meet the criteria for a minimum number of respondents needed and/or has exceeded an acceptable value for coefficient of variance.
  • Out-of-pocket costs include family expenses for premiums, copays, deductibles, and coinsurance for services and prescription drugs. They do not include over-the-counter medications. (Others' definition of OOP spending excludes premiums.)
  • Potentially preventable hospitalizations are defined using the Agency for Healthcare Research and Quality (AHRQ) Patient Quality Indicator (PQI).
  • Preventive care visits include routine care, such as physical examinations and checkups.
  • Single coverage is for individuals.
  • Small group includes enrollees in plans offered by employers with fewer than 50 workers.
  • Statewide average premium represents the unweighted average monthly premium cost across all 19 regions for the second-lowest-cost silver plan for a 40-year-old.
  • Usual source of care refers to the place or provider that an individual typically turns to when medical services are needed.

Regional Breakdowns

  • Bay Area Counties: Alameda, Contra Costa, Marin, Napa, San Francisco, San Mateo, Santa Clara, Solano, and Sonoma
  • Central Coast Counties: Monterey, San Benito, San Luis Obispo, Santa Barbara, Santa Cruz, and Ventura
  • Los Angeles County: Los Angeles
  • Northern and Sierra Counties: Alpine, Amador, Butte, Calaveras, Colusa, Del Norte, Glenn, Humboldt, Inyo, Lake, Lassen, Mariposa, Mendocino, Modoc, Mono, Nevada, Plumas, Shasta, Sierra, Siskiyou, Sutter, Tehama, Trinity, Tuolumne, and Yuba
  • Other Southern Counties: Imperial, Orange, Riverside, San Bernardino, and San Diego
  • Sacramento Area Counties: El Dorado, Placer, Sacramento, and Yolo El Dorado, Placer, Sacramento, and Yolo
  • San Joaquin Valley Counties: Fresno, Kern, Kings, Madera, Merced, San Joaquin, Stanislaus, and Tulare