I’m back at last. I have spent the last few days helping to get my mother buried, in our hearts if not in fact, and only now have time to finish up.
In this post I’ll address the arguments made by David Felson as to the efficacy of glucosamine and chondroitin. Dr. Felson focused mostly on glucosamine for which there is more evidence. His argument was in three parts: he taught us about effect sizes as a way to compare studies; he talked about the GAIT study and issues of subgroup analysis; and he reviewed a meta-analysis done by him and his fellow, Steven Vlad.
Part 4a: Effect Sizes
First, he introduced the concept of the effect size. This is a way of standardizing the results of trials so that they are more directly comparable. It is defined as the difference between outcomes between to trial arms, divided by the standard deviation. It therefore gives the difference in outcome standardized to a normal distribution: a change of 1 represents an improvement of 1 standard deviation for treatment over placebo. This is a large effect of any therapy. An effect size of 0.2 is a small effect, 0.5 a modest effect, and 0.8 a large effect. For comparison, treatment of knee OA with NSAIDs gives an effect size on the order of 0.2-0.3. A total knee replacement – definitive therapy for knee OA – gives an effect size of 1 or greater. Glucosamine has been claimed to have an effect size on the order of 0.3-0.8 depending on the study you read; at least as good and maybe better than NSAIDs. Some studies have shown effect sizes larger than 1 – on the order of magnitude of a knee replacement. Dr. Felson finds this to be simply impossible to believe and I agree.