A 49-year-old man comes to the office for follow-up. A friend was recently diagnosed with gout, and the patient is anxious that he will also develop gout. The patient states that he had read "something about a diet called DASH that reduces the excess of uric acid in the blood and reduces the risk of gout." He would like to try the diet but asks if a less strict version would nevertheless help to reduce his chances of developing gout.
Based on the abstract, if this patient decided to adopt a strict version of the DASH diet (corresponding to the highest fifth intake ranking) as compared to a less strict version of the DASH diet (corresponding to the third fifth intake rating), what proportion of his reduction in risk of gout could be attributed to this intervention?
A)0)28
B)0)50
C)0)72
D)1)00
E)1)38

Question

A 49-year-old man comes to the office for follow-up.  A friend was recently diagnosed with gout, and the patient is anxious that he will also develop gout.  The patient states that he had read "something about a diet called DASH that reduces the excess of uric acid in the blood and reduces the risk of gout."  He would like to try the diet but asks if a less strict version would nevertheless help to reduce his chances of developing gout. 
Based on the abstract, if this patient decided to adopt a strict version of the DASH diet (corresponding to the highest fifth intake ranking) as compared to a less strict version of the DASH diet (corresponding to the third fifth intake rating), what proportion of his reduction in risk of gout could be attributed to this intervention?
A)0)28
B)0)50
C)0)72
D)1)00
E)1)38

Quizplus · Accepted Answer

Explanation: The relative risk reduction (RRR) quantifies the proportion of risk reduction attributable to a specific intervention or exposure as compared to a control. RRR considers the risk for disease in the exposed/intervention group and the unexposed/control group as follows: RRR = (risk in unexposed − risk in exposed) / (risk in unexposed) In this case, the exposed/intervention group is the DASH diet in the highest fifth, and the unexposed/control group is the DASH diet in the third fifth; the risks are reported in person-years (incidence densities). The risk of gout among subjects adopting a DASH diet in the third fifth (unexposed/control group) is 354 / 196,510 = 0.0018, or 1.8 per 1,000 person-years; the risk of gout among subjects adopting a DASH diet in the highest fifth (exposed group) is 252 / 193,455 = 0.0013, or 1.3 per 1,000 person-years. Therefore, the RRR is calculated as: RRR = (1.8 per 1,000 person-years − 1.3 per 1,000 person-years) / 1.8 per 1,000 person-years RRR = 0.5 / 1.8 = ~0.28 (28%) Alternately, RRR is frequently calculated by subtracting the relative risk (RR) from 1: RRR = 1 − RR. RR is the risk of developing a disease (eg, gout) in the exposed group (eg, DASH diet in highest fifth) divided by the risk of developing the same disease in the unexposed group (eg, DASH diet in third fifth). In this case, RR = 0.0013 / 0.0018 = ~0.72 (72%) (Choice C). Therefore, RRR = 1 − 0.72 = 0.28. This means that, compared to patients who adopt a diet DASH diet in the third fifth, patients who adopt a DASH diet in the highest fifth reduce their risk of gout by 28%. (Choice B) The absolute risk reduction (ARR) is defined as the difference in risk between the unexposed and exposed groups. In this case, ARR = 1.8 per 1,000 person-years − 1.3 per 1,000 person-years = 0.5 per 1,000 person-years. (Choice E) If adopting a DASH diet in the third fifth is considered the exposure and adopting a DASH diet in the highest fifth is considered the reference, then RR = 0.0018 / 0.0013 = ~1.38. This means that a DASH diet in the third fifth increases the likelihood of gout by 38% when compared to a DASH diet in the highest fifth. Educational objective: Relative risk reduction may be used to determine which of 2 interventions is more beneficial to reduce the risk of disease based on incidence densities (ie, person-years data). Careful attention is required when identifying the exposed and unexposed groups between 2 interventions.

A 49-Year-Old Man Comes to the Office for Follow-Up