Researchers warn of bias in self-reported anthropometric data
MedWire News: Researchers say that care should be taken when using self-reported measures of body size in epidemiologic analyses, after finding significant differences between self-reported and measured anthropometric data.
"Our study found that self-reported anthropometric data, especially waist and hip circumferences, were biased by actual body size, as well as sociodemographic characteristics," explain Kay-Tee Khaw (University of Cambridge, UK) and colleagues.
"Furthermore, there was a substantial degree of misclassification of body mass index (BMI) and waist circumference categories for both general and central obesity associated with self-reported data," they add.
Using information from the Norfolk arm of the 1993-1997 European Investigation into Cancer and Nutrition Study (EPIC-Norfolk), the team examined the effects of gender, height, weight, age group, educational levels, and social class on differences between self-reported and measured anthropometric data.
Self-reported measures of weight, height, BMI, waist, hip, and waist-to-hip ratio (WHR) for 9933 men and 11,856 women (aged 39-79 years) were obtained from a health and lifestyle questionnaire.
The authors found that overall, men and women overestimated their height by an average of 1.69 and 1.40 cm, respectively, and underestimated their weight by an average of 1.14 and 1.25 kg, their waist circumference by 3.59 and 4.58 cm, their hip circumference by 1.52 and 1.90 cm, and consequently their BMI and WHR, by 0.87 and 0.92 kg/m2 and 0.011 and 0.030, respectively.
Khaw's team showed that generally, shorter people overestimated their height more than taller people, while heavier people underreported their weight and waist and hip circumferences more than lighter people.
Women had a propensity to underreport their weight and waist and hip circumferences more than men, while older people tended to overreport their height and younger people underreport their waist and hip circumference.
Individuals with a higher educational level or of higher social class tended to underestimate their weight, and those with lower levels overestimated their height.
In addition, the researchers found significant misclassifications among BMI categories associated with self-reported data; only 71% of individuals who were overweight according to measured BMI (25-29 kg/m2) reported themselves as overweight, and only 63% of those measured as obese (BMI ≥30 kg/m2) were correctly classified using self-reported values. But the measured data for the 96% of participants who reported being in normal ranges of BMI (18.5-25 kg/m2) showed they had classified themselves correctly.
"[These results] introduce further challenges to interpretation of data, and may account for some of the wide variations in reports on the relationship between different indices of obesity and health outcomes," Khaw et al conclude in the European Journal of Clinical Nutrition.
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By Nikki Withers