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Guyatt G, Rennie D, Meade MO, Cook DJ
Part B Therapy
Chapter 11.4. Surrogate Outcomes
Heiner C. Bucher, Regina Kunz, Deborah J. Cook, Anne Holbrook, Gordon Guyatt
For example, ecologic studies such as the Seven Countries Study16 suggested a strong...

Topics Discussed: angiotensin-converting enzyme inhibitors, anti-arrhythmia agents, coronary heart disease, diabetes mellitus, type 2, diabetic nephropathy, drug class effects, health outcomes, osteoporosis, patient-important outcome, randomized controlled trials, sodium fluoride, statins, surrogate outcomes, target endpoints, validity of evidence

Excerpt: "When we consider the validity of a surrogate endpoint, we must address 2 issues. First, a surrogate outcome will be consistently reliable only if there is a causal connection between change in surrogate and change in the patient-important outcome. Thus, the surrogate must be in the causal pathway of the disease process. For instance, LDL must be a cause of atherosclerotic cardiac and cerebral events to act as a valid surrogate for those events. Second, we must be confident that change in the surrogate captures all critical influences on patient-important outcomes.9 For instance, if the treatment affects either positively or negatively (as turned out to be the case for fibrates13) the morbidity or mortality independent of its effect on LDL, the validity of the surrogate is threatened.To function as a valid substitute for an important target outcome, the surrogate endpoint must be associated with that target outcome. Often, researchers choose surrogate endpoints because they have found a correlation between a surrogate outcome and a target outcome in observational studies. Their understanding of biologic characteristics gives them confidence that changes in the surrogate will invariably lead to changes in the important outcome. The stronger the association, the more likely the causal link between the surrogate and the target. The strength of an association is reflected in statistical measures such as the relative risk (RR) or the odds ratio (see Chapter 7, Does Treatment Lower Risk? Understanding the Results)...."
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