A 65-year-old man comes to the office because his family is concerned about his constant cough after smoking. The patient asks about the risk of developing chronic obstructive pulmonary disease (COPD) in adult smokers. A recent cohort study reported that compared to heavy smokers, the relative risk (RR) of COPD for nonsmokers is 0.10 and for moderate smokers is 0.40. The patient is a moderate smoker. Based on the study, which of the following is the RR of COPD for moderate smokers compared to nonsmokers?

Question

A 65-year-old man comes to the office because his family is concerned about his constant cough after smoking.  The patient asks about the risk of developing chronic obstructive pulmonary disease (COPD) in adult smokers.  A recent cohort study reported that compared to heavy smokers, the relative risk (RR) of COPD for nonsmokers is 0.10 and for moderate smokers is 0.40.  The patient is a moderate smoker.  Based on the study, which of the following is the RR of COPD for moderate smokers compared to nonsmokers?

Quizplus · Accepted Answer

The relative risk (RR) is the measure of association between the exposure to a risk factor and an outcome or disease commonly used in cohort and experimental studies. RR is equal to the risk of an outcome (eg, chronic obstructive pulmonary disease [COPD]) in an exposed group (eg, moderate smokers) divided by the risk of the same outcome in a nonexposed group (eg, nonsmokers). RR_{mod vs non} = (risk of disease in moderate smokers) / (risk of disease in nonsmokers) = Risk_mod / Risk_non In this case, RR_{mod vs non} must be calculated from the RRs for COPD and smoking reported in the given cohort study: RR for nonsmokers compared to heavy smokers: RR_{non vs heavy} = Risk_non / Risk_heavy = 0.10 RR for moderate smokers compared to heavy smokers: RR_{mod vs heavy} = Risk_mod / Risk_heavy = 0.40 RR_{mod vs heavy} and RR_{non vs heavy} have the same comparison group (ie, denominator: Risk_heavy for heavy smokers). Therefore, dividing RR_{mod vs heavy} by RR_{non vs heavy} results in RR_{mod vs non} (ie, Risk_mod / Risk_non). RRmod vs heavyRRnon vs heavy=RiskmodRiskheavy/RisknonRiskheavy/=RiskmodRisknon=RRmod vs nonRRmod vs heavyRRnon vs heavy=RiskmodRiskheavyRisknonRiskheavy=RiskmodRisknon=RRmod vs non Therefore, RR_{mod vs non} = 0.40 / 0.10 = 4. This means that the risk of COPD is four times greater for moderate smokers compared to nonsmokers. (Choice A) 0.10 is the given RR for nonsmokers compared to heavy smokers: RR_{non vs heavy}. (Choice B) 0.25 is the RR for nonsmokers compared to moderate smokers: RR_{non vs mod} = 0.10 / 0.40 = 0.25, meaning that the risk of COPD is 75% (ie, 100% − 25%) lower in nonsmokers compared to moderate smokers. (Choice C) 0.40 is the given RR for moderate smokers compared to heavy smokers: RR_{mod vs heavy}. (Choice D) 2.5 is the RR for heavy smokers compared to moderate smokers (RR_{heavy vs mod}); it is the inverse of the given RR_{mod vs heavy} (ie, RR_{heavy vs mod} = 1 / 0.40 = 2.5). (Choice F) 10 is the RR for heavy smokers compared to nonsmokers (RR_{heavy vs non}); it is the inverse of the given RR_{non vs heavy} (ie, RR_{heavy vs non} = 1 / 0.10 = 10). Educational objective: The relative risk (RR) is the measure of association between the exposure to a risk factor or treatment and an outcome or disease and is commonly used in cohort and experimental studies. The interpretation of the RR depends on which groups are identified as exposed and unexposed.

A 65-Year-Old Man Comes to the Office Because His Family