That Big Childhood Obesity Decline May Have Been a Statistical Error

by Alec Torres

In late February, a report from the U.S. Centers for Disease Control and Prevention announced that obesity rates among children aged 2 to 5 had declined by 40 to 43 percent in the past eight years, a dramatic and encouraging finding. But researchers are now saying that the good news may have been a statistical mistake.

Experts believe the finding may have been in error because other studies have found no such decline in obesity rates within that age group.

Michelle Obama had touted the study as proof that her efforts against childhood obesity are working, and others have credited the reported decline to everything from public-health information campaigns to an increase in breast feeding.

The CDC’s study relied on a set of government-collected data that’s considered highly reliable, but wasn’t ideal for this comparison: The study looked at over 9,000 Americans, but just 871 were between 2 and 5, and just a small proportion of them are obese. The margin of error, in fact, was wide enough that it’s statistically possible there was no decrease at all.