dc.description.abstract | Background: Body mass index (BMI) based on self-reported height and weight has been
criticized as being biased because of an observed tendency for overweight and obese people
to overestimate height and underestimate weight, resulting in higher misclassification for
these groups. We examined the validity of BMI based on self-reported values in a sample of
Norwegian women aged 44–64 years.
Methods: The study sample of 1,837 participants in the Norwegian Women and Cancer study
self-reported height and weight, and then, within 1 year, either self-reported anthropometric
again, or were measured by medical staff. Demographic and anthropometric were compared
using t-tests and chi-square tests of independence. Misclassification of BMI categories was
assessed by weighted Cohen’s kappa and Bland–Altman plot.
Results: On average, the two measurements were taken 8 months apart, and self-reported
weight increased by 0.6 kg (P,0.05), and BMI by 0.2 kg/m2
(P,0.05). The distribution of
BMI categories did not differ between self-reported and measured values. There was substantial
agreement between self-reported values and those measured by medical staff (weighted
kappa 0.73). Under-reporting resulting in misclassification of BMI category was most common
among overweight women (36%), but the highest proportion of extreme under-reporting was
found in obese women (18% outside the 95% limits of agreement). The cumulative distribution
curves for the measured and self-reported values closely followed each other, but measurements
by medical staff were shifted slightly toward higher BMI values.
Conclusion: While there was substantial agreement between self-reported and measured
BMI values, there was small but statistically significant under-reporting of weight and thus
self-reported BMI. The tendency to under-report was largest among overweight women, while
the largest degree of under-reporting was found in the obese group. Self-reported weight and
height provide a valid ranking of BMI for middle-aged Norwegian women. | en_US |