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Modeling the Impact of the Affordable Care Act and the Individual Mandate on Californians


The Patient Protection and Affordable Care Act (ACA) was designed to provide health insurance to uninsured or underinsured individuals. We used the California Simulation of Insurance Markets (CalSIM) model to predict the experience of consumers in California, who will be faced with new insurance options through Medicaid, employer-sponsored insurance, and the individual market in 2014 and beyond. We explored the response and characteristics of Californians who will and will not secure insurance coverage, with and without the “individual mandate” or minimum coverage requirement (MCR). We found 1.8 million Californians (38 %) of the 4.7 million eligible uninsured will secure coverage by 2019 with the MCR, while only 839,000 (18 % of the eligible uninsured) would obtain coverage without it.

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Fig. 1


  1. Premium subsidies to purchase health insurance in the Exchange are available to legal residents of the US with household incomes from 100 % to 400% of FPL who are not otherwise eligible for Medicaid. The subsidies are provided in the form of advance premium tax credits (APTC) on a sliding scale based on the second-lowest premium of a silver-rated (70 % actuarial value) plan. The subsidies effectively cap out-of-pocket premiums to a percentage of each household’s income (2 % for households earning 100–133 % of FPL, 3 % for families earning above 133–150 % of FPL, up to 9.5 % for households earning 400 % of FPL).

  2. The federal law requires that all individual and small group insurance premiums sold in the Exchange or outside of the Exchange must abide by the same premium rating rules. The only variation allowed will be based on age (3:1 ratio within the same plan), smoking status, location, and family size (1.5:1 ratios). In California, smoking status will not be allowed as a premium rating factor.

  3. In raking, the sample weights for each classification are repeatedly adjusted such that the sum of the weights converges to total the marginal distributions. The CalSIM raking procedure adjusts the data to match the marginal and joint distributions of age, socioeconomic status, health status and presence of chronic conditions, race/ethnicity, language, and immigration status in 2009 CHIS. We adjust sample weights from MEPS using the Stata module survwgt described at

  4. In 2013, the Healthy Families Program will be transitioned into Medi-Cal Managed Care plans, meaning that low-income children aged 0–18 will technically be enrolled in Medi-Cal rather than Healthy Families. However, the differences in federal matching funds, cost-sharing requirements, and the federal Children’s Health Insurance Program’s status as an authorized discretionary program rather than a mandatory entitlement like Medicaid make it necessary to continue to differentiate the populations and numbers enrolled in each.


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The authors wish to thank Mr. Richard Figueroa and Mr. Robert Phillips, our project officers at The California Endowment, for their support in developing the CalSIM model and this research. We also thank Dr. Xiao Chen and Mr. Yafeng Zheng of UCLA and Ms. Miranda Dietz of UC Berkeley for their work on the CalSIM model programming and development.

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Correspondence to Dylan H. Roby.

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Roby, D.H., Watson, G., Jacobs, K. et al. Modeling the Impact of the Affordable Care Act and the Individual Mandate on Californians. J Fam Econ Iss 34, 16–28 (2013).

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  • Health Insurance
  • Health Reform
  • Insurance Markets
  • Micro-Simulation
  • Modeling