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Methods and Applications of Statistics in Clinical Trials, Volume 2: Planning, Analysis, and Inferential Methods by N. Balakrishnan

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Chapter 56

Women’s Health Initiative: Statistical Aspects and Selected Early Results

Ross L. Prentice and Garnet L. Anderson

56.1 Introduction

The Women’s Health Initiative (WHI) is perhaps the most ambitious population research investigation ever undertaken. The centerpiece of the WHI program is a randomized, controlled clinical trial (CT) to evaluate the health benefits and risks of three distinct interventions (dietary modification, postmenopausal hormone therapy, and calcium/vitamin D supplementation) among 68,132 postmenopausal women. Participating women were identified from the general population living in proximity to any one of 40 participating clinical centers throughout the United States. The WHI program also includes an observational study (OS) comprising 93,676 postmenopausal women recruited from the same population base as the CT. Enrollment into WHI began in 1993 and concluded in 1998. Intervention activities in the combined hormone therapy component of the CT ended early in July 2002 when evidence had accumulated that the risks exceed the benefits for combined hormone therapy. Follow-up on all participating women is planned through March 2005, giving an average follow-up duration of about 8.5 years in the CT and 7.5 years in the OS.

56.2 WHI Clinical Trial and Observational Study

The WHI CT includes three overlapping components, each a randomized controlled comparison among women who were postmenopausal and in the age range of 50 to 79 at randomization. The dietary ...

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