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: 0.1b

Answer

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.

Work Step by Step

This answer comes from reading the scenario given, and thinking logically based on both the data given and the answer to part (a) of this problem.
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