Exogenous predictors of national performance measures for emergency department crowding.

STUDY
OBJECTIVE: We explore the relationship between exogenous-level predictors and performance on 4 emergency department (ED) throughput measures approved by the National Quality Forum: median ED length of visit for admitted and discharged patients, median waiting time, and rate of left without being seen. We seek to find predictors for benchmarking and public reporting.
METHODS: This was a study of 424 US hospitals that reported data to the National Hospital Ambulatory Care Survey in 2008 to 2009. Wald F tests and generalized linear models were used to test the relationship between exogenous variables (case mix, age mix, ED volume, teaching status, and Metropolitan Statistical Area status) and performance on the measures.
RESULTS: Median waiting time was 35 minutes (95% confidence interval [CI] 26 to 43 minutes), median length of visit for patients treated but not admitted was 131 minutes (95% CI 121 to 142 minutes), median length of visit for patients admitted was 244 minutes (95% CI 218 to 270 minutes), and rate of left without being seen was 1.3% (95% CI 0.9% to 1.8%). Most exogenous variables, including ED volume, Metropolitan Statistical Area, teaching hospital status, age mix, and case mix, demonstrated significant association with waiting times and lengths of visit. Older age and a higher proportion of respiratory complaints were associated with differences in rates of left without being seen.
CONCLUSION: Several exogenous factors outside of a hospital's control are associated with National Quality Forum-approved ED performance measures, which will have important implications for future benchmarking and public reporting of these data.