Surrogate outcomes (March 23, 2005)

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I'm on the mailing list of the Alliance for Human Research Protection, and they highlighted a book review:

for the book

Other reviews of this book appears on the,, and websites:

and in JAMA

The author has his own website:

I have not read this book yet, but I did read several reviews. The thing that caught my eye about the review in Health Affairs was the description of a drug, Fosomax (alendronate) which treats osteoporosis. Although the published literature on this drug looks quite impressive at first, it turns out that you have to treat a large number of women in order to prevent a single hip fracture. Furthermore, although Fosomax improves bone mineral density (BMD), it turns out that

BMD mainly measures the outer layer of bone (cortical bone), whereas much of the strength of bone lies in the inner structures of trabecular bone. Drugs such as Fosamax primarily strengthen cortical rather than trabecular bone, which improves the BMD score but may not contribute as much to fracture prevention.

This is a classic example of a surrogate outcome. Most patients don't care about cortical or trabecular bone density. What they care about is having to endure a broken bone or living with dowager's hump.