14 October 2013

94th percentile

I was subjected to a lengthy lecture by the boys' pediatrician because A2 now sits squarely on the 94th percentile for body mass index (up from the 90th percentile as last year's well visit).

I'm not one of those mothers who cannot see any fault in her children, so I certainly realize that he's differently shaped compared to his brother.  I can even see that his weight exceeds that of peers of the same height so I'm not going to delve into some futile argument about dense bones or unaccounted muscle mass.  Still, 94th percentile seems...off.  It means that in a room of 100 kids his height, only 6 would weigh more than him. 

So I looked into this revered formula created about 175 years ago by a mathematician (i.e., not a physician) whose arbitrary exponent of 2 in the denominator still has some scratching their heads.  BMI is apparently an insensitive measure (where sensitivity indicates true positives and specificity indicates true negatives) that is a terrible predictor variable for important outcomes like cardiovascular and cerebrovascular events as well as mortality in general.  Where it works wonderfully is as a political tool to point at America's slovenliness by the World Health Organization and as a monetary tool by big insurance companies to decline or punish "obese" subscribers.

This isn't to say that I'm not helping him make healthy choices about what he consumes.  I just wish there were other indices outside of BMI. 

Here we are on one of our recent healthy choices, otherwise known as a hike with the dog:






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