Method: Interrupted time series, a quasi-experimental study, was conducted using natural experiment of policy change in California, where Medicaid adult dental coverage was eliminated on July 1, 2009. State Emergency Department Databases (SEDD) for state of California were acquired from Agency for Healthcare Research and Quality (AHRQ) for 2006 to 2011. The database contains information on all ED visits that occurred in California which did not lead to an admission. A non-equivalent dependent variable was used as a control to minimize threats to internal validity. Primary diagnosis ICD-9 codes were used to select ED visits due to dental problems. The study was approved by University of Iowa IRB. Segmented linear regression analyses were conducted using SAS version 9.3.
Result: Before Medicaid adult dental benefits were eliminated, an average of 40.3 enrollees visited an ED per 100,000 enrollees over three and a half years (pre-intervention period). Over the next two and a half years (post-intervention period), an average of 53.4 enrollees visited an ED per 100,000 enrollees. Elimination of adult dental benefits under Medicaid had a statistically significant immediate increase in the proportion of Medicaid adult enrollees who visited ED for dental problem (beta=0.046, p-value=0.0011). There was a significant time trend, i.e. a steady increase in proportion of Medicaid adult enrollees who visited ED for dental problems, throughout the study period (beta=0.0025, p-value<0.0001). However, the policy change did not change this time trend significantly.
Conclusion: The quasi-experimental study provides strong evidence that eliminating Medicaid adult dental benefits in California led to an immediate and significant increase in the proportion of Medicaid adult enrollees who visit an ED for dental problems.