A retrospective, matched-cohort study is conducted to examine the effect of medical care provided by overnight physicians on the outcomes of their scheduled elective procedures performed during the day. Patients undergoing 1 of 5 elective daytime procedures performed by a physician who worked overnight were matched to patients undergoing the same procedure by the same physician on a day when the physician did not work overnight. The study outcome was a composite of patient death and complications. The study reported that the risk of the composite outcome was higher in patients who underwent a daytime procedure performed by a physician who had worked overnight compared to patients who underwent a procedure performed by a physician who had not worked overnight (22% vs. 20%, p = 0.04). Based on these results, what is the approximate percentage of deaths and complications that can be attributed to the physician having worked overnight before the scheduled elective procedures during the day?

Question

A retrospective, matched-cohort study is conducted to examine the effect of medical care provided by overnight physicians on the outcomes of their scheduled elective procedures performed during the day.  Patients undergoing 1 of 5 elective daytime procedures performed by a physician who worked overnight were matched to patients undergoing the same procedure by the same physician on a day when the physician did not work overnight.  The study outcome was a composite of patient death and complications.  The study reported that the risk of the composite outcome was higher in patients who underwent a daytime procedure performed by a physician who had worked overnight compared to patients who underwent a procedure performed by a physician who had not worked overnight (22% vs. 20%, p = 0.04).  Based on these results, what is the approximate percentage of deaths and complications that can be attributed to the physician having worked overnight before the scheduled elective procedures during the day?

Quizplus · Accepted Answer

Explanation: Attributable risk percentage (ARP) describes the percentage of disease in an exposed group that can be attributed to the exposure. It is sometimes described as the percentage of disease in an exposed group that could be prevented by eliminating the exposure (ie, the risk factor). ARP is calculated as the difference in risk of disease between an exposed group and a nonexposed group divided by the risk of disease in the exposed group: ARP = [(Risk_exposed − Risk_nonexposed) / Risk_exposed] × 100 _exposed _nonexposed _exposed In this study, the risk of disease (ie, death and complications) in the exposed (ie, physician worked overnight) group was 22% (or 0.22) (Choice C). In the nonexposed (ie, physician did not work overnight) group, the risk was 20% (or 0.20). Therefore: ARP = [(Risk_exposed − Risk_nonexposed) / Risk_exposed] × 100 = [(0.22 − 0.20) / 0.22)] × 100 = 9.1% _exposed _nonexposed _exposed Therefore, the approximate percentage of deaths and complications that can be attributed to the physician working overnight before the scheduled elective procedures during the day is 9.1%. Alternately, ARP may be calculated using relative risk (RR): ARP = [(RR - 1) / RR] × 100 RR is calculated as the risk of disease in the exposed group divided by the risk of disease in the nonexposed group: RR = (Risk_exposed / Risk_nonexposed) = (0.22 / 0.20) = 1.1 (Choice A) _exposed _nonexposed Therefore: ARP = [(RR − 1) / RR] × 100 = [(1.1 − 1) / 1.1] × 100 = 9.1% This means that among patients who undergo elective daytime procedures, eliminating the risk factor of having physicians who worked overnight perform the procedures could prevent 9.1% of death and complications. (Choice D) Absolute risk increase (ARI) is the difference in the risk of a negative outcome (eg, death and complications) between an exposed (eg, physician worked overnight) group and a nonexposed (eg, physician did not work overnight) group. It is calculated as: ARI = (Risk_exposed − Risk_nonexposed) = (0.22 − 0.20) = 0.02 (or 2%) _exposed _nonexposed Number needed to harm (NNH) is the number of people who must be exposed to a treatment to cause harm to 1 person who otherwise would not have been harmed. It is calculated as: NNH = 1 / ARI = 1 / 0.02 = 50 Educational objective: Attributable risk percentage (ARP) describes the percentage of disease in an exposed group that can be attributed to the exposure. It is calculated as the difference in risk of disease between the exposed and nonexposed groups divided by the risk of disease in the exposed group: ARP = [(Risk_exposed − Risk_nonexposed) / Risk_exposed] × 100 _exposed _nonexposed _exposed

A Retrospective, Matched-Cohort Study Is Conducted to Examine the Effect