In epidemiology, the absolute risk reduction or risk difference is the decrease in risk of a given activity or treatment in relation to a control activity or treatment. It is the inverse of the number needed to treat.
In general, absolute risk reduction is the difference between the control group’s event rate (CER) and the experimental group’s event rate (EER). The difference is usually calculated with respect to two treatments A and B, with A typically a drug and B a placebo. For example, A could be a 5-year treatment with a hypothetical drug, and B is treatment with placebo, i.e. no treatment. A defined endpoint has to be specified, such as a survival or a response rate. For example: the appearance of lung cancer in a 5 year period. If the probabilities pA and pB of this endpoint under treatments A and B, respectively, are known, then the absolute risk reduction is computed as (pB - pA).
The inverse of the absolute risk reduction, NNT, is an important measure in pharmacoeconomics. If a clinical endpoint is devastating enough (e.g. death, heart attack), drugs with a low absolute risk reduction may still be indicated in particular situations. If the endpoint is minor, health insurers may decline to reimburse drugs with a low absolute risk reduction.
Read more about Absolute Risk Reduction: Presenting Results, Worked Example
Famous quotes containing the words absolute, risk and/or reduction:
“As liberty of thought is absolute, so is liberty of speech, which is “inseparable” from the liberty of thought. Liberty of speech, moreover, is essential not only for its own sake but for the sake of truth, which requires absolute liberty for the utterance of unpopular and even demonstrably false opinions.”
—Gertrude Himmelfarb (b. 1922)
“If you love the good thing vitally, enough to give up for it all that one must give up, then you must hate the cheap thing just as hard. I tell you, there is such a thing as creative hate! A contempt that drives you through fire, makes you risk everything and lose everything, makes you a long sight better than you ever knew you could be.”
—Willa Cather (1873–1947)
“The reduction of nuclear arsenals and the removal of the threat of worldwide nuclear destruction is a measure, in my judgment, of the power and strength of a great nation.”
—Jimmy Carter (James Earl Carter, Jr.)