In Reply: Dr Sonnenfeld and colleagues are concerned that a change in the way information on primary expected payer was collected in the NHAMCS between 1997-2004 and 2005-2007 biased our calculation of ED visit rates by payer source. Based on our reassessment, these coding issues do not appear to have affected our findings significantly for several reasons.
First, this change in coding affected the population of people in the United States who had both Medicare and Medicaid (dual eligibles). Due to the way payer source data was collected in NHAMCS, we were only able to identify dual eligibles beginning in 2005. However, there is no reason to believe there was a substantial change in the dual eligible population between 2004 and 2005. In our study, the dual eligible population in 2005 had an estimated 3.1 million visits, or 2.7% of total ED visits. In 2007, the number of visits from dual eligibles was estimated at 3.5 million, or 3.0% of total ED visits. We do not think such a small percentage change over time would significantly alter our findings.