VI. Clinical Relevance

Abstract

In clinical practice, the maneuver that is usually selected is the one that achieves an outcome with at least 10 % of direct superiority or when the number needed to treat is ≈10. Although these parameters serve for estimating the magnitude of an association, we are forced to differenciate the measures of impact (attributable risk, preventable fraction), association (relative risk, odds ratio, risk ratio) and frequency (incidence and prevalence), which are applicable when the outcome is nominal. We also have to identify the way for measuring the strength of association and the magnitude of association when the outcome variable is quantitative. Not unfrequently, association measures are interpreted as if they were impact measures, v.gr., for a relative risk of 0.68, a 32 % of outcome reduction is assumed without considering that this is a relative reduction that can be generated by a ratio of 0.4/0.6, 0.04/0.06 or 0.00004/0.00006 as well; however, the direct reduction is 20 % (60-40 %), 2 % and 2 per 100 000, respectively. Therefore, in order to estimate the impact of a maneuver, it is important that the direct difference or the number needed to treat is available.