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(Stroke. 2009;40:S71.)
© 2009 American Heart Association, Inc.

Prevention 2: High-Risk Populations

High-Risk Populations

Introduction

From the Department of Biostatistics (G.H.), University of Alabama, Birmingham, Ala; and the Department of Neurology (R.L.S.), University of Miami, Miami, Fla.

Correspondence to George Howard, University of Alabama at Birmingham, Professor and Chair, Department of Biostatistics, Ryals Building, Room 327, 1665 University Blvd, Birmingham, AL 35294-0022. E-mail ghoward@uab.edu

Key Words: prevention • high-risk populations

An extract of the first 250 words of the full text is provided, because this article has no abstract.

The study of primary prevention of stroke in the general population is a challenge for several reasons. Sample sizes to provide a sufficient number of events to address hypotheses of interest are usually prohibitively large, mainly because stroke events in the general population over age 45 occur at a rate below 1% annually.¹ For example, to detect a hazard ratio of 1.5 with 90% power for a risk factor that is 10% prevalent would require a study with 711 stroke events.² With an incidence rate of less than 1%, this implies that a study would have to accrue more than 71100 person-years exposure (ie, following 20000 individuals for more than 3 years). That is, although we think of stroke being unfortunately common, its "low" incidence in the general population makes studies of primary prevention prohibitively large and expensive. This is likely a major contributor to the fact that most NIH-funded intervention trials have focused on secondary stroke prevention, where stroke event rates are many times higher and study sample sizes are many times smaller.

These challenges of primary prevention trials, however, may be more than offset when the rewards of successful primary prevention efforts are considered. For two complementary reasons the public health value of preventing a first stroke is many times greater than prevention of secondary stroke: (1) because the number of people at risk is larger, the absolute number of primary strokes is greater than secondary events, and (2) the impact on reducing disability is much greater because . . . [Full Text of this Article]