Confirmation Procession

Confirming Another Victory against Childhood Obesity

Late this week, headlines proclaiming another victory against childhood obesity flowed from a study of severe obesity in public elementary and middle schools of New York City. Researchers from the NYC Department of Health concluded that their efforts to reduce obesity brought the prevalence of severe childhood obesity down by 9.5% in these school children between 2006 and 2011.

Who doesn’t want to cheer about this victory?

National trends for severe childhood obesity have been going in the wrong direction for some time. Earlier this year, Asheley Skinner and Joseph Skelton published an analysis of the latest NHANES data for childhood obesity that showed an accelerating rate of growth in Class 3 (severe) childhood obesity.

Could it be that New York City is bucking the national trend?

Possibly. The city’s Department of Health has certainly been an innovative model for programs to reduce the impact of obesity in both children and adults.

But it’s also worth considering the possibility of confirmation bias. Quite naturally, people favor results that confirm their beliefs and wishes.

Ashelely Skinner of the UNC School of Public Health, who was not involved in this study, points out that it’s worth paying attention to the biologically implausible values (BIVs) that were excluded from this analysis. She tells us:

The most important thing about reading this article is the concept of “biologically implausible values.” The point is that BIVs should identify measurement error. The headline — and the decline — is only seen when excluding the BIVs. When including them, the prevalence is actually increasing.

In other words, as severe childhood obesity has grown, we can no longer assume that a BMI above 50 is an implausible value for a child.

We certainly hope that New York City, through innovative efforts, has found the secret sauce for bringing severe childhood obesity down. But for now, we’re keeping the cork in our bottle of champagne.

Click here to read more from Reuters and here to read the study.

Confirmation Procession, photograph © Todd Ehlers / flickr

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