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Centre for Evidence-
Based Medicine

Example NNTs - General Surgery

Condition or Disorder Intervention vs. Control Outcome Follow-up Duration Event Rates % NNT (95% CI)
Hip and knee arthroplasty1 Patients were allocated to a clinical pathway group (received "proactive" treatment where specific daily goals were set for the patient) vs. control group (received "reactive" treatment where the healthcare team provided care in response to the patient's conditions and wants) Complications (wound infection, chest infections deep venous thrombosis, joint dislocation, decubitus pressure areas, failure to cope at home and decreased range of motion after discharge) 3 months 28.2 10.9 6 (4 to 19)
Postoperative abdominal wound infection2 Impervious wound-edge protector vs. no wound edge protector (control) All wounds 30 days 30 14 7 (4 to 13)
Clean-contaminated wounds (minor interruption in aseptic technique or minor spillage from the gastrointestina 1 tract) 13 7 Not significant
Contaminated wounds (major interruption in aseptic technique or susequent spillage 67 24 3 (2 to 6)
Dirty wounds (gross fecal spillage) 94 75 Not significant
Hip surgery3 Aspirin vs. placebo Symptomatic deep venous thrombosis 35 days 1.5 1 232 (140 to 2239)
Pulmonary embolism 1.2 0.7 195 (140 to 466)


  1. Med J Aust. 18 Jan 1999; 170: 59-62
  2. Lancet. May 8, 1999; 353: 1585
  3. Lancet. Apr 15, 2000; 355: 1295-302