Friday, September 18, 2009

Effect Magnitude

Everybody knows some things are good for health and some things are bad.  Yet one rarely learns the magnitude of the positive or negative effect, making it impossible to take the logical approach, which is to balance risks and benefits as we make all sorts of choices.

For example, how much benefit will I receive if I eat organic food, compared to standard food?  How much risk (and what type?) if I drink water out of nalgene/lexan bottles containing Bisphenol A?

For some risks, epidemiologists have done a great job measuring magnitude.  In 1976, you had about a 1 in 100,000 chance of developing Guillain Barre Syndrome (GBS) in the 6-8 weeks post-vaccination.  Not a high risk:  but devastating if you are the one affected.

Were other autoimmune conditions caused by the vaccine?  We don't know, as the intensive case ascertainment performed for GBS was not performed for anything else.  GBS happened fast and got your attention; a less dramatic illness developing over a longer window of time would be less likely to be noticed.

This week's BMJ titled a news article with the claim that Swine flu vaccine is a "thousandfold" safer than the infection, say experts.  But where are the completed safety studies?  The studies in children have only been going on for 3-4 weeks, and in pregnant women for less time.  What black hole was this number pulled from?

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