RT Journal Article
SR Electronic
T1 Potential for bias in waiting time studies: events between enrolment and admission
JF Journal of Epidemiology and Community Health
JO J Epidemiol Community Health
FD BMJ Publishing Group Ltd
SP 891
OP 894
DO 10.1136/jech.55.12.891
VO 55
IS 12
A1 B Sobolev
A1 P Brown
A1 D Zelt
YR 2001
UL http://jech.bmj.com/content/55/12/891.abstract
AB STUDY OBJECTIVE To demonstrate the effect of exclusion of data on delays in scheduling operations in calculating difference in admission rates between two enrolment periods. DESIGN A prospective cohort study; outcome measure—waiting time for elective admission; study variables—enrolment periods, before 31 March 1997 and after that date; the time of scheduling delay; gender; age; urgency, and type of surgery. SETTING An acute care hospital in Ontario, Canada. PARTICIPANTS 1173 consecutive cases accepted for elective vascular surgery between 1 July 1994 and 31 March 1999. MAIN RESULTS Before adjustment for scheduling delays, a 20% lower admission rate was associated with period 2, rate ratio (RR) = 0.8 (95% confidence intervals (CI)= 0.7, 0.9). The difference between the periods became only marginally significant after the adjustment, RR = 0.9 (95% CI=0.8, 1.0). No difference between the periods was found when admission rates were compared before a delay occurred, RR = 0.9 (95% CI=0.8, 1.1). In delayed patients, those enrolled in period 1 and 2 had, respectively, a 40% and a 60% lower admission rate than the period 1 patients admitted without scheduling delays, RR = 0.6 (95% CI=0.4, 0.8) for period 1 and RR = 0.4 (95%CI=0.3, 0.5) for period 2. CONCLUSIONS The results provide evidence that patients experiencing a delay in scheduling operation have a lower admission rate after the event. Thus, potential for bias exists when between group comparison of waiting time is done without adjustment for an intermediate event that may occur before elective admission.