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This woe for the state of education came bubbling up again as I read a comment on a PBS article about the measles outbreak in Indiana. Allie Morris, the author of the article, wrote that at least 13 of the individuals who had contracted measles had a history of MMR vaccine refusal. The commenter, Mmavallet, couldn't believe this number, suggesting that it was statistically impossible for there to be 13 individuals who were all unvaccinated, coupled with a belief that the vaccine couldn't be 95% effective (it's not, BTW, being >99% effective):I don't buy that all 13 people spread over various counties were all unvaccinated. And the MMR does not have a 95% efficacy rate or else you wouldn't be having these outbreaks in a population where 98% of people vaccinate. It's statistically impossible. If you really research the numbers on these outbreaks, about 50% of those infected are vaccinated! If they really worked, you wouldn't have to continually get revaccinated for the same illness. It's not immunity if it wears off...only natural immunity is permanent.Let's take a closer look at the issue, shall we?
Basically, the problem involves figuring out a couple of fractions and percentages. We might all remember story problems asking us to figure out that X is what percentage of Y? Or, alternatively, X is Z percent of what? And yet another variation, what is Z percent of Y? This can be boiled down into a simple equation:X/Y = %/100To address this individual's comment, we would need to start with a few basic assumptions. First, that the vaccine is 95% effective (we'll do this with a 99% figure, as well). Second, we need to know about how virulent measles is; in other words, what percentage of vulnerable people would be infected if exposed? According to the CDC, that attack rate is about 90%. Finally, we need to know what the approximate uptake rate is for the vaccine. The commenter claims that 98% of individuals in the area vaccinate. We'll use that number for our calculations.
Sunday, March 04, 2012
Harpocrates Speaks: Of Maths and Measels
When it comes to loony causes, I have to rank the anti-vax pro-disease nutters as some of the looniest... And a good tell-tale signal that a cause is loony is the level of deception that they will use to twist and distort facts. The creationists are a good example of this. However, Todd W. has written a great article about the way that the pro-disease anti-vaxers seem to try to abuse math to support their lies.