The Basic Practice of Statistics 7th Edition

Published by W. H. Freeman
ISBN 10: 1-46414-253-X
ISBN 13: 978-1-46414-253-6

Chapter 0 - Getting Started - Chapter 0 Exercises - Page 9: 0.1b


A "healthy user" bias affects the randomized controlled trial results because, while people who took Vitamin E supplements were observationally healthier, this was due to other lurking variables such as exercise and other healthy lifestyle traits. When tested in a randomized controlled study, some of the subjects would not have these healthy traits, and would therefore still be at a higher risk despite the Vitamin E.

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