Mathematical health policy models, including microsimulation models (MSMs), are widely used to simulate complex processes and predict outcomes consistent with available data. Calibration is a method to estimate parameter values such that model predictions are similar to observed outcomes of interest. Bayesian calibration methods are popular among the available calibration techniques, given their strong theoretical basis and flexibility to incorporate prior beliefs and draw values from the posterior distribution of model parameters and hence the ability to characterize and evaluate parameter uncertainty in the model outcomes. Approximate Bayesian computation (ABC) is an approach to calibrate complex models in which the likelihood is intractable, focusing on measuring the difference between the simulated model predictions and outcomes of interest in observed data. Although ABC methods are increasingly being used, there is limited practical guidance in the medical decision-making literature on approaches to implement ABC to calibrate MSMs. In this tutorial, we describe the Bayesian calibration framework, introduce the ABC approach, and provide step-by-step guidance for implementing an ABC algorithm to calibrate MSMs, using 2 case examples based on a microsimulation model for dementia. We also provide the R code for applying these methods.

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Older adults may receive either or a combination of unpaid family/friend and paid caregiving. The consumption of family/friend and paid caregiving may be sensitive to minimum wage policies. We used data ( n = 11,698 unique respondents) from the Health and Retirement Study and a difference-in-differences design to evaluate associations between increases in state minimum wage between 2010 and 2014 and family/friend and paid caregiving consumed by adults age 65+ years. We also examined responses to increases in minimum wage for respondents with dementia or Medicaid beneficiaries. People living in states that increased their minimum wage did not consume substantially different hours of family/friend, paid, or any family/friend or paid caregiving. We did not observe differential responses between increases in minimum wage and hours of family/friend or paid caregiving among people with dementia or Medicaid beneficiaries. Increases in state minimum wage were not associated with changes in caregiving consumed by adults age 65+.