When Michelle Obama celebrated the fourth anniversary of "Let's Move," her White House initiative on fitness and healthy eating, she cited a recent study by the Centers for Disease Control (CDC) showing a remarkable 43 percent drop in obesity rates among children ages 2-5. Mrs. Obama brought up the study again on Friday at a Partnership for a Healthier America’s Building a Healthier Future Summit. But a report by Reuters health & science correspondent Sharon Begley casts doubt on the validity of the results of the study. While Begley concludes that "no one can say for certain that the claim is wrong," the results are so uncertain that "based on the researchers' own data, the obesity rate may have even risen rather than declined."
The problem lies in large measure with the small sample size of the CDC study and its relatively large margin of error. Begley explains:
The 13.9 percent obesity rate among preschoolers reported for 2003-2004 had a large enough margin of error that the actual rate could range between 10.8 percent and 17.6 percent, the CDC authors acknowledged. The 8.4 percent rate in 2011-2012 reported could range from 5.9 percent and 11.6 percent.
Since the range for 2003-2004 overlaps with that of 2011-2012, [epidemiologist Geoffrey Kabat of the Albert Einstein College of Medicine in New York City] said, "that's another way of saying there might have been no change" in preschoolers' obesity rate. Even an increase is a statistical possibility.
The study size is not the only problem. Other studies, some with considerably larger sample sizes, have shown significantly smaller decreases; others have shown little change; still others have actually shown obesity increasing. For instance, a study of 200,000 children in the WIC (Women, Infants and Children) program "found virtually no change in obesity rates":
Rather than reducing the prevalence of obesity among 3-and-4-year olds in the WIC program in California's Los Angeles County, researchers found that the problem worsened from 2003 to 2011. Obesity rose to 20.4 percent from about 17 percent, the researchers reported in the CDC's Morbidity and Mortality Weekly Report in 2013.
In New York, the WIC study found that obesity rates fell to 15.5 percent in 2011 from about 19.5 percent in 2003, a much less dramatic drop than the 40 percent decline.
"We agree there is a slight downward trend in obesity among 2-to-5-year olds," said Shannon Whaley, a co-author of the WIC study. "But a 43 percent drop is absolutely not what we're seeing."
This is not the first time Mrs. Obama has cited statistics in support of Let's Move that turned out to be less than meets the eye. Just last year, on the third anniversary of Let's Move, the first lady's office sent out a press release that appeared to take credit for the recent developments that "national childhood obesity rate has leveled off, and even declined in some cities and states." In particular, the White House highlighted a 13 percent decline in childhood obesity in Mississippi. But as we reported at the time:
[t]he 13 percent decrease that Mrs. Obama touted is measured from Spring 2005 through Spring 2011. “Let's Move” was launched in February 2010, so the first five years of the time period in question were prior to Let's Move's existence.
This week's Reuters report questioning the 43 percent decline suggests one more reason to question the results showing a decline in pre-schooler obesity rates:
[F]ew anti-obesity efforts target preschoolers...