Understanding and Interpreting the National Hospital Ambulatory Medical Care Survey: Key Questions and Answers

Abstract

SEE EDITORIAL, P. 722. Editor’s Note: The National Hospital Ambulatory Medical Care Survey (NHAMCS) is widely used for medical research. Nearly 500 articles have been published based on this database, including 28 in Annals of Emergency Medicine. NHAMCS is a national probability sample survey of visits to emergency and outpatient departments in nonfederal, general, and short-stay hospitals, conducted by the Centers for Disease Control and Prevention, National Center for Health Statistics (http://www.cdc.gov/nchs/ahcd.htm). Strengths of the NHAMCS survey are its rigorous methodology, nationally representative nature, large size, wide array of variables, and capacity to examine long-term trends. Investigators can freely download the database and test locally developed hypotheses. Challenges with NHAMCS are that, given its logistic and statistical complexity, resulting research can be difficult for readers to interpret and for editors and reviewers to critique. There are important limitations and caveats to this survey that, if overlooked, could lead to misleading or inaccurate conclusions. In this article, we have a posed a series of questions to 2 NHAMCS statisticians, and we believe that their answers will be invaluable to both NHAMCS investigators and readers of its research.