Monumental Illusion

Discovering Anew the Flaws in Self-Reports

Sad but true, we often have to learn the same things over and over again. So it is with a basic fact of obesity prevalence. State health officials get comfortable with relying upon self-reports. Often, that’s all they have. It’s easier to do a telephone or online survey than to actually collect measurements of height and weight. But then along comes a dose of actual measurements and harsh reality. That happened in Florida and Wisconsin recently. So health officials in those states rediscovered the flaws in self-reports for height and weight.

Understating Prevalence by Nine to Ten Percent

Florida officials thought that their obesity rate was 28%. That’s not great, but it’s not bad when headlines tell you the national rate is 40%. However, those national numbers come from actual measurements. The state figure came from telephone surveys conducted for the BRFSS.

Unfortunately, that’s a bogus comparison. When researchers analyzed data from electronic health records recently, they came up with a more accurate reading on obesity prevalence in Florida – 37%. That’s not very different from the national rate.

A similar finding surfaced in Wisconsin recently. Researchers found that the rate there was not 31%, as previously reported. Instead, data from actual measurements showed the prevalence is 41%

Inconsistent Misreporting

You can dismiss the headlines about “higher rates than previously thought” as naive if you like. Health officials are well aware that self-reports understate obesity prevalence. People think of themselves as taller and thinner than reality.

But the real problem comes when you try to compare self-reports across different regions and time periods. People fudge the numbers for a reason. Stigma motivates misreporting. When stigma grows, misreporting can grow with it. Misreporting can be different in different regions. We saw that in a 2013 study that showed more misreporting in north central states like Wisconsin than in southern states like Alabama.

So beware of scorecards that use self-reported data. Those numbers are wobbly.

Click here for more on the Florida rates and here for more on the Wisconsin rates. For the studies behind these headlines, click here and here.

Monumental Illusion, photograph © Frans Persoon / flickr

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June 19, 2018

One Response to “Discovering Anew the Flaws in Self-Reports”

  1. June 19, 2018 at 10:14 am, David Stone said:

    The other classic self-reporting bias: under-reporting Cals consumed and over-reporting physical activity. One of my nutrition profs from long ago, Doris Calloway, used to say “When you bring into the metabolic ward obese patients who swear they cannot lose weight no matter how few Cals they eat and feed them what they say they eat, they lose weight.”

    Moreover, it wouldn’t be surprising to find that self-reporting of any behavior that is considered undesirable (drinking, smoking, other drug use, couch-potato-hood among the lean, eating junk food, etc.) would tend to be under-reported regardless of body weight.