Between 1980 and 2010 in the United States, childhood obesity more than doubled in children and tripled in adolescents, according to the Centers for Disease Control and Prevention (CDC). By 2010, more than one third of U.S. children and adolescents were deemed overweight or obese, the CDC says.
As alarming as such statistics sound, they may actually understate the problem, according to a study co-authored by Alison Buttenheim, an alumna (2009-2011) of the Robert Wood Johnson Foundation (RWJF) Health & Society Scholars program at the University of Pennsylvania. Buttenheim and colleagues found that children and adolescents often fail to report their height and weight in population surveys, and that omission may distort national estimates of how many actually are overweight or obese.
“We already knew that when kids self-report their height and weight, they don’t do a very good job—they report with error,” says Buttenheim, PhD, MBA, an assistant professor of nursing at the University of Pennsylvania School of Nursing in Philadelphia. What previous studies had not factored in, she says, is that some youngsters didn’t state a height and weight at all.
Buttenheim says her research found that “it’s not just a random selection of kids who aren’t reporting those vital statistics. It tends to be kids who are heavier, and younger.” When those youngsters’ information isn’t included in population calculations, the resulting statistics on obesity prevalence may understate the problem, she says.
The data’s accuracy matters because it guides U.S. efforts to address obesity and its health consequences. Obese youth are at a greater risk for cardiovascular disease, pre-diabetes, and bone and joint problems, the CDC reports. They also are likely to be obese as adults, and therefore more at risk for heart disease, type 2 diabetes, stroke, osteoarthritis, and several types of cancer.
The study Buttenheim co-authored, “Underestimation of Adolescent Obesity,” was published in the May/June 2013 edition of the journal Nursing Research.
For the study, Buttenheim and colleagues used data gathered between August 2006 and December 2008 via the Los Angeles Family and Neighborhood Survey (L.A.FANS), a longitudinal study of approximately 3,000 households in Los Angeles County, California.
Working with a survey sample of more than 600 White, Black, and Hispanic youths ages 12-17, the researchers analyzed height and weight data. They compared the measures taken by trained assessors to the vital statistics that youngsters self-reported, paying particular attention to youngsters who refused to answer or said “don’t know” when asked their height and weight.
In public health and population surveys, “a lot of the time we don’t have actual measurements, so we need to know how far off the self-reported estimates are,” Buttenheim says. With the L.A.FANS measurements as the benchmark, the study could assess the relative accuracy of the information provided by self-reporters. But more, the study could fill in some blanks about the non-reporters—not only their height and weight, but other characteristics.
“Failure to report may occur for many reasons,” says the study report. “Adolescents, particularly at younger ages, may not know their current height and weight because of recent growth spurts. Limited healthcare access may yield fewer opportunities to be weighed or measured in a clinical setting. Parents, particularly those with lower levels of education, may be less concerned with monitoring children’s height and weight.”
The report also suggests that “selective nonresponse” may occur because “adolescents who are uncomfortable with their body size may be reluctant to reveal their height or weight.” If youngsters who fail to report also tend to be youngsters who are heavier, then relying on self-reports would “further compromis(e) validity” of obesity prevalence statistics, the researchers reasoned.
In the L.A.FANS sample of 12- to 17-year-olds, Buttenheim and colleagues repeatedly found what they called “gaps” between the measured heights and weights of those youngsters who did and did not self-report. “In this study, adolescents with higher BMI (body mass index) were less like to report height and weight,” the researchers report. “Among younger teens, measured obesity prevalence was higher for those who did not report height and weight compared with those who did, 40 percent versus 30 percent.”
Buttenheim says she was particularly struck by the findings on the youngest subjects in the study. “Younger adolescents (ages 12-13 years), in particular, were both less likely than older adolescents to report height and weight and less likely to estimate height and weight correctly when they did report these measures,” the study report says. When researchers compared the weight status of the younger adolescents who did and did not report height and weight, obesity prevalence was 33 percent higher for the non-reporters.
To Buttenheim, “the biggest implication from this study is the need to think about how we collect self-reported height and weight data. The results we published make me ask: ‘What can we do so fewer kids will fail to answer those questions, and fewer will answer with such huge error?’”
The study authors suggest possible remedies to the problem. One is to measure study participants rather than rely on self-reports but, as the authors acknowledge, “measurement is expensive and only possible in face-to-face interviews.” A second option would be to seek the body mass information from parents rather than youngsters, but “previous research strongly indicated that parents misreport (and perhaps misperceive) children’s body size” as well, the authors say.
A third option, Buttenheim says, is to improve interview tools and techniques so that fewer kids will say they “don’t know” because they’re apprehensive about sharing personal data. Reducing the proportion of non-responses will be key, she says, “to having valid population estimates so we can identify problems, design interventions, and then evaluate their impact in a population where we’re concerned about this rising obesity prevalence.”
Buttenheim’s co-authors on the study, “Underestimation of Adolescent Obesity,” were Noreen Goldman, DSc, and Anne R. Pebley, PhD.
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