Relative risk RR

The relative risk is defined again as a ratio, this time in relation to the risks calculated for the two treatments. For the trastuzumab group the risk is the proportion of patients suffering SAEs which takes the value 117/1677 = 0.070 while for the observation only group this is 81/1710 = 0.047. The relative risk (RR) (sometimes called the risk ratio) is then the ratio of these risks  

There are also conventions with relative risk. As with the odds ratio we usually put the risk for the test treatment group as the numerator and the risk for the control group as the denominator. But now, because we are calculating risk there should be no confusion with regard to what we view as the event we tend to calculate relative risk and not relative benefit. 

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Having a second-degree relative affected increases a woman s risk of developing breast cancer by approximately 50% [relative risk (RR) = 1.5]. 

TABLE 9.2. RELATIVE RISKS (RR) AND PREDICTIVE VALUES OF TESTS FOR POLYMORPHIC FORMS FOR ADRS OR... 

Typically statisticians use one of the three approaches to represent treatment differences for such data absolute rate reduction (ARR), relative risk (RR) and the odds ratio (OR). 

The Canadian Implantable Defibrillator Study studied ICD therapy versus amiodarone while CASH studied ICD therapy versus a variety of antiarrhythmic medications in patients with resuscitated SCD. Both trials found nonsignificant reductions in mortality with ICD implantation. CIDS showed a relative risk (RR) reduction of 19.7% [p = 0.14] and CASH showed a RR reduction of 23% in mortality [p = 0.08]. 

A complication arises, however, when we consider simultaneous exposure to two or more chemicals, e.g., asbestos and cigarettes. The relative risks (RR) of lung cancer in persons exposed to one or both of these agents (Selikoff, 1977) are as follows ... 

Blair et al. (1998) performed a retrospective cohort mortality study of 14 457 workers employed for at least one year between 1952 and 1956 at an aircraft maintenance facility in the United States. Among this cohort were 6737 workers who had been exposed to carbon tetrachloride (Stewart et al., 1991). The methods used for this study are described in greater detail in the monograph on dichloromethane. An extensive exposure assessment was performed to classify exposure to trichloroethylene quantitatively and to classify exposure (ever/never) to other chemicals qualitatively (Stewart et al., 1991). Risks from chemicals other than trichloroethylene w ere examined in a Poisson regression analysis of cancer incidence data. Among women, exposure to carbon tetrachloride was associated with an increased risk of non-Hodgkin lymphoma (relative risk (RR), 3.3 95% CI,... 

Two studies evaluated the effects of lipid-lowering therapy on clinical endpoints in the leg. The Program on the Surgical Control of the Hyperlipidemias was a randomized trial of partial ileal-bypass surgery for the treatment of hyperlipidemia in 838 patients (9). After five years, the relative risk (RR) of an abnormal ankle-brachial index value (ABI) was 0.6 (95% Cl, 0.4 to 0.9, absolute risk reduction, 15% points, p < 0.01), and the RR of claudication or limb-threatening ischemia was 0.7 (95% Cl, 0.2 to 0.9, absolute risk reduction, 7% points, p < 0.01), as compared with the control group. 

Relative measures of exposure (referred to as relative risks ) are measures of the strength of an association. The relative risk (RR) compares the likelihood of developing disease in the exposed group to the likelihood of developing disease in... 

Figure 26.1. Measuring the strength of an association relative risk (RR).

Figure 7.1 The design of a cohort study and its relationship with case-control study designs. Individuals who died during follow-up in the shaded area are eligible for inclusion in a case-control study including incident cases between t and t2- The controls in the case-control study are individuals who did not have the disease of interest at the time of involvement. Arrows indicate end of follow-up, either because of (a) loss to follow-up, (b) mortality due to cause of interest, or (c) other causes of death. The risk ratio, or relative risk (RR) = ( died cause of interest in exposed/E person years)/( died cause of interest controls/E person years)...

Relative Risk (RR)— The risk expressed as a ratio of the incidence of diseased subjects exposed to a particular risk factor to the incidence of diseased subjects in a non-exposed referent group. 

Analysis and Interpretation In a case-control study it is possible to compare the frequencies of exposures in the cases and controls. However, what one is really interested in is a comparison of the frequencies of the disease in the exposed and the unexposed. The latter comparison is usually expressed as a relative risk (RR), which is defined as... 

The results of randomized controlled trials comparing two drags can be used to generate a statistic called the relative risk (RR) (Table 2). This is a ratio of the risk of an outcome with one treatment and the risk of the same outcome with the other treatment. 

In any case the epidemiologist tries to match, and then worries a lot about uncontrolled factors that may confound interpretation of the study results. The numbers of new cases of disease or deaths per unit of exposed and non-exposed population, per unit of time - the disease incidence or mortality rates - are obtained and compared for the two populations. This comparison yields the Relative Risk (RR). Elevated RRs, as with elevated ORs for the case-control studies, suggest a relationship between exposure and disease. 

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