Introduction to propensity scores: A case study on the comparative effectiveness of laparoscopic vs open appendectomy.
OBJECTIVE
To demonstrate the use of propensity scores to evaluate the comparative effectiveness of laparoscopic and open appendectomy.


METHODS
Retrospective cohort study.


METHODS
Academic and private hospitals.


METHODS
All patients undergoing open or laparoscopic appendectomy (n = 21 475) in the Public Use File of the American College of Surgeons National Surgical Quality Improvement Program were included in the study. We first evaluated the surgical approach (laparoscopic vs open) using multivariate logistic regression. We next generated propensity scores and compared outcomes for open and laparoscopic appendectomy in a 1:1 matched cohort. Covariates in the model for propensity scores included comorbidities, age, sex, race, and evidence of perforation.


METHODS
Patient morbidity and mortality, rate of return to operating room, and hospital length of stay.


RESULTS
Twenty-eight percent of patients underwent open appendectomy, and 72% had a laparoscopic approach; 33% (open) vs 14% (laparoscopic) had evidence of a ruptured appendix. In the propensity-matched cohort, there was no difference in mortality (0.3% vs 0.2%), reoperation (1.8% vs 1.5%), or incidence of major complications (5.9% vs 5.4%) between groups. Patients undergoing laparoscopic appendectomy experienced fewer wound infections (odds ratio [OR], 0.4; 95% confidence interval [CI], 0.3-0.5) and fewer episodes of sepsis (0.8; 0.6-1.0) but had a greater risk of intra-abdominal abscess (1.7; 1.3-2.2). An analysis using multivariate adjustment resulted in similar findings.


CONCLUSIONS
After accounting for patient severity, open and laparoscopic appendectomy had similar clinical outcomes. In this case study, propensity score methods and multivariate adjustment yielded nearly identical results.
Department of Surgery, University of Michigan Medical School, Ann Arbor, 48109-5033, USA. mhemmila@umich.edu
Mark R
MR
Hemmila
Nancy J
NJ
Birkmeyer
Saman
S
Arbabi
Nicholas H
NH
Osborne
Wendy L
WL
Wahl
Justin B
JB
Dimick
D000328:Adult; D001062:Appendectomy / Q000379:methods*; D001064:Appendicitis / Q000453:epidemiology / Q000601:surgery*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D010535:Laparoscopy / Q000379:methods*; D007813:Laparotomy / Q000379:methods*; D007902:Length of Stay / Q000639:trends; D008297:Male; D009017:Morbidity / Q000639:trends; D012189:Retrospective Studies; D015996:Survival Rate / Q000639:trends; D014481:United States / Q000453:epidemiology