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Absolute risk is one of the most understandable ways of communicating health risks to the general public. [2] In difference to absolute risk, the relative risk (RR) is the ratio of the probability of an outcome (probability) in an exposed group to the probability of an outcome in an unexposed group.
The relative risk reduction is 0.5 (50%), while the absolute risk reduction is 0.0001 (0.01%). The absolute risk reduction reflects the low probability of getting colon cancer in the first place, while reporting only relative risk reduction, would run into risk of readers exaggerating the effectiveness of the drug. [5]
The relative risk (RR) or risk ratio is the ratio of the probability of an outcome in an exposed group to the probability of an outcome in an unexposed group. Together with risk difference and odds ratio , relative risk measures the association between the exposure and the outcome.
It is calculated as = / = /, where is the incidence in the exposed group, is the incidence in the unexposed group, and is the relative risk. [2] It is used when an exposure increases the risk, as opposed to reducing it, in which case its symmetrical notion is preventable fraction among the unexposed .
Hyperbolic absolute risk aversion (HARA) is the most general class of utility functions that are usually used in practice (specifically, CRRA (constant relative risk aversion, see below), CARA (constant absolute risk aversion), and quadratic utility all exhibit HARA and are often used because of their mathematical tractability).
If the risk of an adverse event is increased by the exposure rather than decreased, the term relative risk increase (RRI) is used, and it is computed as () /. [ 1 ] [ 2 ] If the direction of risk change is not assumed, the term relative effect is used, and it is computed in the same way as relative risk increase.
where R C is the absolute risk of the unexposed group. If the rare disease assumption does not apply, the odds ratio may be very different from the relative risk and should not be interpreted as a relative risk. Consider the death rate of men and women passengers when a ship sank. [3] Of 462 women, 154 died and 308 survived.
It is defined as the inverse of the absolute risk increase, and computed as / (), where is the incidence in the treated (exposed) group, and is the incidence in the control (unexposed) group. [1] Intuitively, the lower the number needed to harm, the worse the risk factor, with 1 meaning that every exposed person is harmed.