INTRODUCTION: There has been concern of increased emergency department (ED) 
length of stay (LOS) during the months when new residents are orienting to their 
roles. This so-called "July Effect" has long been thought to increase LOS, and 
potentially contribute to hospital overcrowding and increased waiting time for 
patients. The objective of this study is to determine if the average ED LOS at 
the beginning of the hospital academic year differs for teaching hospitals with 
residents in the ED, when compared to other months of the year, and as compared 
to non-teaching hospitals without residents.
METHODS: We performed a retrospective analysis of a nationally representative 
sample of 283,621 ED visits from the National Hospital Ambulatory Medical Care 
Survey (NHAMCS), from 2001 to 2008. We stratified the sample by proportion of 
visits seen by a resident, and compared July to the rest of the year, July to 
June, and July and August to the remainder of the year. We compared LOS for 
teaching hospitals to non-teaching hospitals. We used bivariate statistics, and 
multivariable regression modeling to adjust for covariates.
RESULTS: Our findings show that at teaching hospitals with residents, there is 
no significant difference in mean LOS for the month of July (275 minutes) versus 
the rest of the year (259 min), July and August versus the rest of the year, or 
July versus June. Non-teaching hospital control samples yielded similar results 
with no significant difference in LOS for the same time periods. There was a 
significant difference found in mean LOS at teaching hospitals (260 minutes) as 
compared to non-teaching hospitals (185 minutes) throughout the year (p<0.0001).
CONCLUSION: Teaching hospitals with residents in the ED have slower throughput 
of patients, no matter what time of year. Thus, the "July Effect" does not 
appear to a factor in ED LOS. This has implications as overcrowding and patient 
boarding become more of a concern in our increasingly busy EDs. These results 
question the need for additional staffing early in the academic year. Teaching 
hospitals may already institute more robust staffing during this time, 
preventing any significant increase in LOS. Multiple factors contribute to long 
stays in the ED. While patients seen by residents stay longer in the ED, there 
is little variability throughout the academic year.