b. Smokers had 17% more lung cancers compared to non-smokers. Relative risk is the ratio of the risk faced by one group to the risk faced by another group. (Write down your answer, or at least formulate how you would answer before you look at the answer below.). Common terms to describe these ratios are, Frequently, the term "relative risk" is used to encompass all of these. d. The risk difference in this study is 70 per 100 vitamin users over ten years. A risk ratio > 1 suggests an increased risk of that outcome in the exposed group. Altman DG (1991) Practical statistics for medical research. Note that the "exposure" of interest was low-dose aspirin, and the aspirin group is summarized in the top row. 4 th ed. At the conclusion of the study the investigators found a risk ratio = 17. Measures of disease frequency can be compared by calculating their ratio. When RR < 1, % decrease = (1 - RR) x 100, e.g. The relative risk and odds ratio of 1 suggests that there is no difference between two groups. All Rights Reserved. The incidence of coronary artery disease in those who take vitamins C & E daily is 0.70 (or 70%). The risk of myocardial infarction among subjects taking aspirin was 0.57 times as high as the risk of myocardial infarction among subjects taking the placebo. The relative risk is a ratio and does not follow a normal distribution, regardless of the sample sizes in the comparison groups. Since the relative risk is a simple ratio, errors tend to occur when the terms "more" or "less" are used. return to top | previous page | next page, Content ©2018. Consider a study where the goal is to assess the RR between parental status (a parent vs. not a parent) and intelligence level (low intelligence vs. high intelligence). Relative Risk is very similar to Odds Ratio, however, RR is calculated by using percentages, whereas Odds Ratio is calculated by using the ratio of odds. risk is a ratio of event probabilities. (Rate ratios are often interpreted as if they were risk ratios, e.g., post-menopausal women using HRT had 0.47 times the risk of CAD compared to women not using HRT, but it is more precise to refer to the ratio of rates rather than risk.). Which of the following is a correct interpretation of this finding? The RR is estimated as the absolute risk with the risk variable divided by the absolute risk in the control group. Thus, the estimate of the relative risk is simply 13.7%/8.2% = 1.668. It requires the examination of two dichotomous variables, where one variable measures the event (occurred vs. not occurred) and the other variable measures the groups (group 1 vs. group 2). The findings are as follows: - The frequency of bronchitis in the smokers is 27 per 1,000 person-years. the ratio of median times (median ratio) at which treatment and control group participants are at some endpoint. It should be clear that the hazard ratio is a relative measure of effect and tells us nothing about absolute risk. In this study patients who underwent incidental appendectomy had 4.2 times the risk of post-operative wound infection compared to patients who did not undergo incidental appendectomy. There were 17 more cases of lung cancer in the smokers. They followed these physicians for about five years. The calculated RR was reported to be 0.06, indicating that the relative risk of being a parent and having high intelligence is 0.06 times that of people who are parents and have low intelligence. The relative risk (RR) of an event is the likelihood of its occurrence after exposure to a risk variable as compared with the likelihood of its occurrence in a control or reference group. In all cases, statistical significance is assumed if the 95% confidence interval (CI) around the relative risk does not include 1.0. Subjects who underwent incidental appendectomy had 4.2, Subjects who underwent incidental appendectomy were 4.2. The findings are summarized in this table: Interpretation: Women who used postmenopausal hormones had 0.47 times the rate of coronary artery disease compared to women who did not use postmenopausal hormones. In essence, we regard the unexposed group as having 100% of the risk and express the exposed group relative to that. Is it those who didn't take any aspirin, those who took low-dose aspirin but used it irregularly, those who took high dose aspirin, those who took acetaminophen...? Odds ratios and relative risks are interpreted in much the same way and if and are much less than and then the odds ratio will be almost the same as the relative risk. e. 17% of the lung cancers in smokers were due to smoking. RR and OR are commonly used measures of association in observational studies. c. Smokers had 17 times more risk of lung cancer than non-smokers. Relative Risk (RR) is often used when the study involves comparing the likelihood, or chance, of an event occurring between two groups. Relative Risk is considered a descriptive statistic, not an inferential statistic; as it does not determine statistical significance. '' is used to investigate the effects of hormone replacement therapy ( HRT on... Of 1.0 indicates no difference between two groups ( the risk difference in this study 70... Reduction of risk. ) statistical term used to describe the chances of a state, behavior or strategy compared. 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