Normal Limits

"Chance is the very guide of life"

"In practical medicine the facts are far too few for them to enter into the calculus of probabilities... in applied medicine we are always concerned with the individual" -- S. D. Poisson

March 30, 2006

Evidence-based rock, paper, and scissors

Non-transitive dice, invented by Stanford statistician Professor Bradley Efron, defies intuition. In one version, it consists of a sequence of 4 dice A, B, C, D, each with non-standard numbers of its 6 faces. The numbers are chosen such that no matter which die of the 4 you pick, all I need to do is to pick the one before it (e.g., if you picked C then I'll pick A, or if you picked A then I'll pick D), and then, on our next throws of the dice, I am guaranteed to beat you 2/3 of the time. There is no trickery. The dice are not mechanically loaded; the numbers work out so. But this non-transitivity is disconcerting and boggles the mind.

We see something similar in the mediacl research literature. In the Feb issue of the Journal of American Psychiatry, Dr. Heres et al reviewed head-to-head comparisons of 2nd-generation antipsychotics. The report, titled Why olanzepine beats risperidone, risperidone beats quetiepine, and quetiepine beats olanzepine, studied 42 trials that were designed to each compare two 2nd-generation antipsychotics. Published results of these trials were assessed by a psychiatrist and an internist who were blinded to the identity of the medications. They evaluated whether the report favored one drug of the other, and a host of other potential sources of bias in these studies.

Some interesting findings:

  1. 33 trials (out of 42) were sponsored by pharmaceutical companies: No surprise here. In fact they thought these industry-sponsored trials were generally of better quality as far as design, implementation, and sample size are concerned.

  2. 90 percent of these trials favored the medication sold by the sponsoring pharm company

The wording of the abstract is also systematically different. In those abtracts in which the medication sold by the sponsoring company was shown to be superior, the findings would be elaborated in detail towards the end of the abstract. On the other hand, those trials with results unfavorable to the sponsor only briefly mentions the ersult at the beginning of the abstracts.

All in all not as surprising as the transitive dice.

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james gaulte said...

I'm glad to see your site active again.
The tricks and traps of EBM are of great interest to me and your posts typically educate and encourage more thought about the topics raised.

Ming-Chih said...

Thanks for the encouragement, Dr Gaulte! I've always enjoyed your thoughtful and insightful posts.