The attributable risk is the risk of an event that is specifically due to the risk factor of interest.Ĭalculation. Presumably, sexual dysfunction resulting from venlafaxine treatment involves specific drug-related mechanisms, whereas sexual dysfunction with placebo involves nocebo mechanisms, illness-related factors, or other causes.Ĭoncept. Similarly, the absolute risk of developing sexual dysfunction with placebo is 3/36, or 8.3%.Įxpressed in plain English, 20.0% of patients who receive venlafaxine (as administered in this trial) and 8.3% of those who receive placebo (as administered in this trial) can expect to experience new-onset sexual dysfunction during the first 8 weeks of treatment. Using the data in Table 1, because 40 patients took venlafaxine and because 8 of them developed sexual dysfunction, the absolute risk of sexual dysfunction with venlafaxine is 8/40, or 20.0%. It can also be expressed in terms of person-years of exposure to the risk factor. This figure is usually expressed as a percentage, though it can also be expressed in other ways, such as per 1,000 or per 100,000 persons in the population at risk. The absolute risk of an event is estimated as the number of persons who actually experience the event divided by the total number of persons exposed to the risk of that event. The absolute risk of an event is the likelihood of occurrence of that event in the population at risk.Ĭalculation.
Using these data, we can calculate the values for a variety of terms, as illustrated in the sections that follow.Ĭoncept.
During the trial, new-onset sexual dysfunction was identified in 8 patients treated with venlafaxine and in 3 patients treated with placebo. Whereas the terms may be applied slightly differently in different explanatory texts, the general principles are the same.Ĭonsider a hypothetical RCT in which 76 depressed patients were randomly assigned to receive either venlafaxine (n = 40) or placebo (n = 36) for 8 weeks. Nevertheless, similar principles operate when these concepts are applied in epidemiologic research. Readers may note that the explanations and examples provided apply mostly to randomized controlled trials (RCTs), cohort studies, and case-control studies. Whereas these and related terms have been well explained in many articles, 1-5 this article presents a version, with examples, that is meant to be both simple and practical. Many research papers present findings as odds ratios (ORs) and relative risks (RRs) as measures of effect size for categorical outcomes. © Copyright 2015 Physicians Postgraduate Press, Inc.
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