Relative risk reduction RRR

Consider the data presented in table 4.4 relating to the binary outcome died/survival in a parallel group trial. 

When the relative risk is less than one, as in this case, we often also calculate the reduction in the relative risk  

In this example RRR = 0.43, there is a 43 per cent reduction in the risk (of death) in the active group compared to control. 

We tend to use RRR where the intervention is having a benefit in reducing the risk. In the earlier example involving trastuzumab and the incidence of patients suffering SAEs, the active treatment was associated with an increase in risk. We could speak in terms of a relative risk increase (RRI) of 0.47(= 1.47— 1), a 47 per cent increase in the risk of suffering SAEs, but this tends not to be done. 

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The Safety of Tirofiban in Acute Ischemic Stroke (SaTIS) trial examined 250 patients 6-22 hours after stroke onset treated with tirohban infusion or placebo for 48 hours. No increase in ICH was reported in the active group. Although no beneht in early functional recovery was observed, 5-6-month mortality was lower in the tirohban-treated group (relative risk reduction (RRR) 27%, 95% Cl 0.08-0.95, p = 0.03). 

The efficacy of clopidogrel as an antiplatelet agent in atherothrombotic disorders was demonstrated in the CAPRIE trial. In this study of more than 19,000 patients with a history of either myocardial infarction (MI), stroke, or peripheral arterial disease (PAD), clopidogrel 75 mg/day was compared with aspirin 325 mg/day for its ability to decrease MI, stroke, or cardiovascular death. In the final analysis, clopidogrel was slightly (8% relative risk reduction [RRR]) more effective than aspirin (p =. 043) and had a similar incidence of adverse effects. It is not associated with the blood dyscrasias (neutropenia) common with its congener, ticlopidine, and is used widely in patients with atherosclerosis. 

In 1994, the benefit of fibrinolytic therapy in the treatment of the elderly was brought into question by the Fibrinolytic Therapy Trialists (FTT) Collaborative Group (3). This meta-analysis included nine fibrinolytic trials incorporating over 58,600 patients. Of these patients, 17,000 were 65-74 years of age and 5754 were >75 years of age. This analysis revealed that the benefit of fibrinolytic therapy diminished with advancing age relative risk reduction (RRR) of death associated with fibrinolytic therapy was 22% in patients <55 years of age, 19% in patients 55-64 years of age, 16% in patients 65-74 years of age and only 4% in patients >75 years of age. However, while the relative effectiveness of fibrinolytic therapy diminished with advancing age, the 4% RRR translated into a 1% ARR, or NNT = 100, still a clinically important difference and similar to the 1.2% ARR in patients <55 years of age. Therefore, even small relative reductions in risk can be important when applied to groups with increased risk. 

AECAPS/TexCAPS = Air ForceAexas Coronary Atherosclerosis Prevention Study (Downs et ah, 1998) Helsinki = The Helsinki Heart Study (Frick et al., 1 987) LRC-CPPT = The Lipid Research Clinics Coronary Primary Prevention Trial (insull et al., 1984) Oslo = The Oslo Study (Hjermann et ah, 1988) WOSCOPS = The West of Scotland Coronary Prevention Study (Shepherd et al., 1995) ALLHAT = Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial approximately 13-15% of patients had a history of coronary heart disease (CHD) events are CHD events only WHI = Women s Health initiative RRR = relative risk reduction ARR = absolute risk reduction NNT = number needed to treat NA = not available CEE = conjugated equine estrogen MPA = medroxyprogesterone acetate CARDS = Collaborative Atorvastatin Diabetes Study (presented at the 2004 American Diabetes Association meeting). 

RRR Relative risk reduction TC Total cholesterol TG Triglycerides TGF Transforming growth factor... 

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