We're all Lake Woebegonians now.

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From this morning's New York Times:

"Nationally, about 17 percent of children under 20 are obese, or about 12.5 million people, according to the Centers for Disease Control and Prevention, which defines childhood obesity as a body mass index at or above the 95th percentile for children of the same age and sex."

There must be some explanation for this.  Comments definitely open.


  1. Jerry Friedman said,

    December 11, 2012 @ 12:25 pm


    Without checking, I'd guess it's the 95th percentile as calculated in some previous year.

    [Fixed now. Thanks, Paul]

  2. David L said,

    December 11, 2012 @ 12:29 pm

    Looking at the CDC page you link to, and links therein, it seems that the BMI percentiles are defined on age- and sex-specific growth charts developed in 2000/2001. So my guess is that 17% of children today are now defined as obese, according to standards developed over a decade ago. That's believable, but of course it doesn't solve the problem of how to define obesity in a population whose BMI distribution is constantly evolving.

  3. Jeff Carney said,

    December 11, 2012 @ 12:30 pm

    Clearly, the population of people aged 0-19 exceeds 100% of the population of children under twenty. This explains overcrowded classrooms as well.

  4. Jongseong Park said,

    December 11, 2012 @ 12:31 pm

    From the link, it looks like they use the 2000 CDC growth chart.

  5. Peter M Reed said,

    December 11, 2012 @ 12:32 pm

    Maybe they are using old BMI stats as a reference level. From the guidance paper in Pediatrics [Expert Committee Recommendations Regarding the Prevention, Assessment, and Treatment of Child and Adolescent Overweight and Obesity: Summary Report, Pediatrics Vol. 120 No. Supplement 4 December 1, 2007
    pp. S164 -S192 ]:

    "On the basis of measured heights and weights from nationally representative samples of US children assessed approximately every 5 years, obesity prevalence has increased from ∼5% in 1963 to 1970 to 17% in 2003 to 2004.4"

    The 5% figure in 1963 makes a lot more sense for those above the 95th percentile level. Since then they kept those 1963 figures as the population shifted fatter?

    Just guessing really, as all the charts on the CDC site (http://www.cdc.gov/growthcharts/clinical_charts.htm) seem to have been published since 2000.

  6. Ginger Yellow said,

    December 11, 2012 @ 12:36 pm

    As far as I can make out from a quick scan of this document, it's based on data from surveys from the 60s to the 90s (p 15).

  7. Nancy Friedman said,

    December 11, 2012 @ 1:06 pm

    Forgive me for being picky and tangential, but it's Lake Wobegon, not Woebegon, where all the children are above average.

  8. Andy Averill said,

    December 11, 2012 @ 1:10 pm

    None of this is particularly useful anyway. BMI doesn't take into account the difference between muscle mass and fat. And defining obesity in terms of percentiles just means that as kids get fatter on average, the definition of what constitutes an unhealthy weight keeps changing. Lake Wobegon, indeed.

  9. George said,

    December 11, 2012 @ 1:16 pm

    I think it may be explained by another frequently observed modern condition, that of the infantilized twenty and thirty somethings. Thus the definition at the 95th percentile includes children of all ages.

    That 25 year old post grad returnee who is stuck upstairs on the xbox is positively lithe. It's just the genuine young ones that tend to obesity

  10. MonkeyBoy said,

    December 11, 2012 @ 1:18 pm

    Averill: BMI doesn't take into account the difference between muscle mass and fat.

    BMI does serve as a valid statistical proxy for obesity because maybe 95% of people classified as BMI-obease are actually obese.

  11. Jay said,

    December 11, 2012 @ 1:32 pm

    MonkeyBoy: Define your terms! What is "actually obese"?

  12. Anna said,

    December 11, 2012 @ 1:58 pm

    This comment thread hasn't been derailed enough yet, so here's an entertaining essay on BMI and why it has no actual basis in science:


  13. Sili said,

    December 11, 2012 @ 2:15 pm

    Clearly, the population of people aged 0-19 exceeds 100% of the population of children under twenty. This explains overcrowded classrooms as well.

    That would also help to explain why teenage pregnancies fall off steeply for twenty-year-olds.

  14. YM said,

    December 11, 2012 @ 2:24 pm

    Adults under 20, however, are getting scrawnier.

  15. Irina said,

    December 11, 2012 @ 2:29 pm

    Perhaps 12% of children are clustered right on the 95th percentile.

  16. Jo Walton said,

    December 11, 2012 @ 5:27 pm

    I'm pretty sure that what it rationally means is that according to statistical probability, only 5% of the target population will be obese, but in fact 12% are.

  17. Bryant said,

    December 11, 2012 @ 6:03 pm

    > at or above the 95th percentile for children of the same age and sex.

    Note that "the same nationality" isn't listed, while 17% is explicitly a national statistic—so the 95th percentile could be calculated using some larger-than-national population.

  18. RP said,

    December 11, 2012 @ 6:27 pm

    "Children under 20" – as though a 19-year-old might be a child!

    The OED says the word "child" originally meant a baby, and was gradually extended to mean a young person below the age of puberty, and later still "extended to youths approaching or entering upon manhood". The OED does not say when it was extended to 19-year-olds. But there are some jurisdictions where the age of majority is still 21, so perhaps in those places the word "child" is used in this way.

  19. Matthew said,

    December 11, 2012 @ 10:47 pm

    I actually got really confused by this when I read about it yesterday. Then I realized that there are children in other countries. That made the most sense to me.

  20. Vicki said,

    December 11, 2012 @ 11:14 pm

    This is like the archeologists' term "Before Present," which doesn't mean what it sounds like. FDR died 5 years B.P, because "present" is fixed at 1950 C.E.

  21. Pete Schult said,

    December 12, 2012 @ 4:15 am

    Clearly, the article was from media on Gallifrey, where the top 5% is bigger on the inside.

  22. Jerry Friedman said,

    December 12, 2012 @ 10:42 am

    @Nancy: What is it about us Friedmans?

    @Pete Schult: The further in you go, the bigger it gets.

  23. Circe said,

    December 12, 2012 @ 1:59 pm


    Wikipedia suggests the moniker "Before Physics" has been suggested for "Before Present (BP)". I hope this catches on. We might also consider "Before Mathematics" (fixed at the beginning of the Babylonian era?) an "Before Linguistics" (fixed at Panini's birth?).

  24. KWillets said,

    December 12, 2012 @ 2:41 pm

    Wobegon sounds suspiciously like the Ojibwe word for lake, zaaga'igan. Apparently it's just a coincidence, but a better-than-average one.

  25. brian said,

    December 14, 2012 @ 2:40 pm

    I suspect it's the commonly played tactic of adding 'obese and overweight' together and pretending that they are the same thing. That's 15% and a slight clustering on the top end of the scale, would make this add up on a spreadsheet.

  26. Peter said,

    December 15, 2012 @ 5:43 am

    The first thing that occurred to me is that it might be a global baseline, or at least much broader than just the US — but it seems like it's actually old US numbers, as so many are saying.

    To the commenter who said BMI doesn't distinguish enough between muscle and fat, I think that's less of a confounding factor in children, right?

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