Who breaches the four-hour emergency department wait time target?:A retrospective analysis of 374,000 emergency department attendances between 2008 and 2013 at a type 1 emergency department in England
Background: The four-hour target is a key hospital emergency department performance indicator in
England and one that drives the physical and organisational design of the ED. Some studies have
identified time of presentation as a key factor affecting waiting times. Few studies have investigated
other determinants of breaching the four-hour target. Therefore, our objective was to describe patterns
of emergency department breaches of the four-hour wait time target and identify patients at highest
risk of breaching.
Methods: This was a retrospective cohort study of a large type 1 Emergency department at an NHS
teaching hospital in Oxford, England. We analysed anonymised individual level patient data for
378,873 emergency department attendances, representing all attendances between April 2008 and
April 2013. We examined patient characteristics and emergency department presentation
circumstances associated with the highest likelihood of breaching the four-hour wait time target.
Results: We used 374,459 complete cases for analysis. In total, 8.3% of all patients breached the
four-hour wait time target. The main determinants of patients breaching the four-hour wait time target
were hour of arrival to the ED, day of the week, patient age, ED referral source, and the types of
investigations patients receive (p<0.01 for all associations). Patients most likely to breach the four-
hour target were older, presented at night, presented on Monday, received multiple types of
investigation in the emergency department, and were not self-referred (p<0.01 for all associations).
Patients attending from October to February had a higher odds of breaching compared to those
attending from March to September (OR 1.63, 95% CI 1.59 to 1.66).
Conclusions: There are a number of independent patient and circumstantial factors associated with
the probability of breaching the four-hour ED wait time target including patient age, ED referral
source, the types of investigations patients receive, as well as the hour, day, and month of arrival to
the ED. Efforts to reduce the number of breaches could explore late-evening/overnight staffing, access
to diagnostic tests, rapid discharge facilities, and early assessment and input on diagnostic and
management strategies from a senior practitioner