NCPA - National Center for Policy Analysis

Has Preschool Obesity Really Fallen?

March 21, 2014

The preschool obesity rate has likely not fallen 43 percent, despite a recent Centers for Disease Control and Prevention (CDC) study, says Reuters.

In February, the CDC published a study finding that preschool obesity has dropped 43 percent in just 10 years. The news was surprising to experts, and for good reason: according to all other research, the obesity rate has not dropped, and in fact may have risen.

When the report was published in the Journal of the American Medical Association, anti-obesity activists cheered federal nutrition changes and the elimination of trans-fats, with the First Lady and others seeing the study as vindication that national efforts to curb childhood obesity were, in fact, working.

However, obesity specialists have looked at the data used and say that it could be a statistical fluke. Similar studies, they say, have not found a remotely similar decrease.

  • The study used data from the National Health and Nutrition Examination Survey (NHANES). Conducted every year since the 1960s, NHANES involves in-person interviews and physical exams.
  • Obesity is defined by the CDC as having a body mass index (BMI, which is a ratio of weight to height) above 30. For children, the calculation is a little different, as the obesity measurement depends on age and sex.
  • The survey used data from 2011-2012, involving 9,120 people, 871 of which were ages 2 to 5 years old. While 871 might be a large number in some types of research, having a fairly low obesity rate and only a few hundred people in a sample could result in errors.
  • In the 2003-2004 study, the obesity rate was 13.9 percent for preschoolers. That dropped to 8.4 percent in 2011-2012, according to the NHANES data.
  • But the margin of error for the 2003-2004 year was large, and the real obesity figure could have ranged from 10.8 percent to 17.6 percent.
  • For 2011-2012, the number could have been anywhere from 5.9 percent to 11.6 percent.

Because those ranges overlap, it's possible that there could have been no change at all in the preschool obesity rate. Or, the rate could actually have increased.

Other studies have found no change in obesity rates, and some have even found that the problem has worsened. Without more data, scientists say that they cannot be sure whether the CDC report is accurate.

Source: Sharon Begley, "A Plunge in U.S. Preschool Obesity? Not So Fast, Experts Say," Reuters, March 16, 2014.


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