In anticipation of upcoming health care legislation, the RAND Corporation developed a microsimulation model to forecast the responses of individuals, families and firms to such legislation. The COMPARE (COMPrehensive Assessment of Reform Efforts) microsimulation has been used to estimate the impact of major policy changes in the United States, such as the Affordable Care Act on uninsurance rates, participation in the group and the non-group insurance markets, firms' insurance offer rates, enrollment in public programs such as Medicaid and CHIP, private insurance premiums and costs to the federal and state governments.

Background. Computer models played an important role in the health care reform debate, and they will continue to be used during implementation. However, current models are limited by inputs, including available data. Aim. We review microsimulation and cell-based models. For each type of model, we discuss data requirements and other factors that may affect its scope. We also discuss how to improve models by changing data collection and data access procedures. Materials and Methods. We review the modeling literature, documentation on existing models, and data resources available to modelers. Results. Even with limitations, models can be a useful resource. However, limitations must be clearly communicated. Modeling approaches could be improved by enhancing existing longitudinal data, improving access to linked data, and developing data focused on health care providers. Discussion. Longitudinal datasets could be improved by standardizing questions across surveys or by fielding supplemental panels. Funding could be provided to identify causal parameters and to clarify ranges of effects reported in the literature. Finally, a forum for routine communication between modelers and policy makers could be established. Conclusion. Modeling can provide useful information for health care policy makers. Thus, investing in tools to improve modeling capabilities should be a high priority.

The Affordable Care Act changed the regulations governing small firms' health insurance premiums. However, small businesses can avoid many of the new regulations by self-insuring or maintaining grandfathered plans. If small firms with healthy and lower-cost enrollees avoid the regulations, premiums for coverage sold through insurance exchanges could be unaffordable. In this analysis we used the RAND Comprehensive Assessment of Reform Efforts microsimulation model to predict the effects of self-insurance and grandfathering exemptions on coverage and premiums available through the exchanges. We estimate that Affordable Care Act regulations restricting employers' ability to offer grandfathered plans will result in lower premiums on plans available through the exchanges and will have small negative effects on enrollment in the exchanges. Our results suggest that these regulations are essential to keeping premiums on the Small Business Health Options Program (SHOP) exchanges affordable. Our analysis also found that Affordable Care Act regulations limiting self-insurance will reduce enrollment in the exchanges somewhat, without substantially affecting exchange premiums.

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The process by which Congress considers legislation rarely affords the public an opportunity to examine how the outcomes might change if components of the law were structured differently. We evaluated how the recently enacted health reform law performed relative to a large number of alternative designs on measures of effectiveness and efficiency. We found that only a few different approaches would produce both more newly insured people and a lower cost to the government. However, these are characterized by design options that seemed political untenable, such as higher penalties, lower subsidies, or less generous Medicaid expansion.