Users' Guides to the Medical Literature
Guyatt G, Rennie D, Meade MO, Cook DJ
Part B Therapy
Chapter 7. Does Treatment Lower Risk? Understanding the Results
Roman Jaeschke, Gordon Guyatt, Alexandra Barratt, Stephen Walter, Deborah J. Cook
Relative Risk vs Risk Difference: Why the Fuss?
Topics Discussed:
measures of effect, risk differences, risk ratios (relative risk), risk reduction, understanding the results
Excerpt:
"Failing to distinguish between the OR and the RR when
interpreting randomized trial results will seldom mislead
you; you must, however, distinguish between the RR and
the RD. The reason is that the RR is generally
far larger than the RD, and presentations of results in
the form of RR (or RRR) can convey a misleading message.
Reducing a patient's risk by 50% sounds
impressive. That may, however, represent a reduction in risk from
2% to 1%. The corresponding 1% RD sounds
considerably less impressive...."
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