Emergency department (ED) overcrowding in Canada is an ongoing problem resulting in prolonged wait times, service declines, increased patient suffering, and adverse patient outcomes. We explored the relationship between socioeconomic status (SES) and ED use in Canada's universal health care system to improve our understanding of the nature of ED users to both improve health care to the most deprived populations and reduce ED patient input.

This retrospective study took information from the National Ambulatory Care Reporting System (NACRS) database for all ED visits in Ontario between April 1, 2003, and March 31, 2010. As there is no direct measure of SES available from ED visit records, a proxy measure of SES was used, namely a deprivation index (DI) developed from material and social factors from the 2006 Canadian census using the patient's residential neighbourhood. DI scores were assigned to ED visit records using Statistics Canada's Postal Code Conversion File, which links postal and census geography.

A total of 36,765,189 visits occurred during the study period. A cross-province trend was found wherein the most deprived population used EDs disproportionately more than the least deprived population (relative risk: 1.971 95% confidence interval 1.969–1.973, p < 0.0001). This trend was stable across the entire study period, although the divergence is attenuating.

Social determinants of health clearly impact ED use patterns. People of the lowest SES use ED services disproportionately more than other socioeconomic groups. Focused health system planning and policy development directed at optimizing health services for the lowest SES populations are essential to changing ED use patterns and may be one method of decreasing ED overcrowding.