Clarity on childhood obesity rates

A deeper look into a study reveals no significant changes

The author is a research analyst for Chico State’s Center for Nutrition & Activity Promotion.

A recent New York Times headline based on an obesity study was a jaw-dropper: “Obesity Rate for Young Children Plummets 43% in Decade.”

But that Feb. 25 headline does not accurately portray what the study says.

That 43 percent plummet represents the relative decline in preschool obesity rates between two groups of toddlers, one in 2003-04 and the other in 2011-12. Obesity in this age group dropped from 13.9 percent to 8.1 percent, an absolute difference of 5.8 percent but a relative percentage decline of 43 percent (5.8 percent divided by 13.9 percent).

Imagine 100 toddlers at a preschool. Visualizing 43 percent of those preschoolers makes most of us mentally count 43 kids, or almost half of the total. Yet expressed in percentage terms, about 14 (13.9 percent) of the first 100 kids were obese compared to eight (8.1 percent) in the final group of 100 kids, for a difference of six kids (5.8 percent). That’s a 43 percent drop (6 divided by 14), but it’s still just six kids.

Trumpeting a 43 percent change grabs front-page headlines, but isn’t an accurate representation of the findings. By comparing only the two most statistically advantageous data points in the series—the beginning and the end—the analysis ignored everything in between. Numbers actually rose and fell during that decade, suggesting a less obvious trend.

Also, the reported error margins are large enough and overlap in such a way that they can’t rule out the possibility of an obesity increase between 2003-04 and 2011-12.

So the point is—as the study concludes—“Overall, there have been no significant changes in obesity prevalence in youth or adults between 2003-2004 and 2011-2012.”

The likelihood of obesity has increased, in fact, for adolescents (ages 12-17) from low-income homes, according to recent analysis of the same data reported in the Proceedings of the National Academy of Science.

This is not to say people, including those of us at Chico State’s Center for Nutrition & Activity Promotion (CNAP), aren’t working hard to change things. In fact, CNAP has been working to improve community health for more than a decade. We’re ready for good news.

Very soon CNAP will begin its latest major health education initiative, assisting the California Department of Public Health and public health departments throughout Northern California in reversing obesity trends. Please join us in helping make that New York Times headline come true one day soon—for all age groups.