The first lady, Michelle Obama, was quick to grab credit for a study showing a whopping 43% decline in childhood obesity:

“Today’s announcement reaffirms my belief that together, we are making a real difference in helping kids across the country get a healthier start to life,” the first lady said in a statement.  

“We know how essential it is to set our youngest children on a path towards a lifetime of healthy eating and physical activity, and more than 10,000 childcare programs participating in the Let’s Move! Child Care initiative are doing vitally important work on this front. Yet, while this announcement reflects important progress, we also know that there is tremendous work still to be done to support healthy futures for all our children.” (The Hill)

Unfortunately for Michelle, the study now looks like an anomaly at best, junk science at the worst. Sharon Begley of Reuters:

If the news last month that the prevalence of obesity among American preschoolers had plunged 43 percent in a decade sounded too good to be true, that's because it probably was, researchers say. (snip)

…as obesity specialists take a closer look at the data, some are questioning the 43 percent claim, suggesting that it may be a statistical fluke and pointing out that similar studies find no such decrease in obesity among preschoolers.

In fact, based on the researchers' own data, the obesity rate may have even risen rather than declined.

"You need to have a healthy degree of skepticism about the validity of this finding," said Dr. Lee Kaplan, director of the weight center at Massachusetts General Hospital in Boston.

No evidence of the kinds of major shifts in the behavior among preschoolers aged 2 to 5 exists which would explain a 43 percent drop in their obesity rates, he said.

In fact, in rushing to grab credit, Michelle O overlooked the researchers’ specific warnings about the limitations of their data:

To be sure, the CDC scientists were aware of the statistical limitations of their data, and their paper clearly stated that the findings were imprecise.

The 43 percent headline figure refers to the drop from the 13.9 percent rate in 2003-04 to the 8.4 percent rate in 2011-2012. The change of 5.5 points represents a decline of 40 percent from the original 13.9 percent. (The 43 percent trumpeted by a CDC press release comes from rounding those numbers to 14 and 8, respectively.)

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.

It looks to em like the first lady’s claims are an example of shovel-ready BS.