| Summary: | Objective. To assess the validity of self-reported body
mass index in the National Health Survey.
120 participants were selected and questioned
about their weight and height with exactly the same questions
that the National Health Survey uses. Afterwards, and once
informed consent was obtained, participants were weighed and
measured, and this data was used as the gold standard.
On average, participants underestimated their
weight by 1.39 kg, overestimated their height by 0.55 cm and
underestimated their body mass index by 0.71 kg/m2. The
sensitivity of self-reported self reported body mass index (BMI)
to detect overweight was 77%, the specificity was 97%, the
positive predictive value was 0.95 and the negative predictive
value was 0.86. The Kappa index was 0.76 and the quadratically
weighted Kappa index was 0.85. The correlation coefficient
between self-reported and measured BMI was 0.96 and the intraclass
correlation coefficient was 0.97.
Self-reported data is an efficient way of
obtaining information about BMI, although with limitations,
because self-reported data tends to underestimate weight and
overestimate height, thus underestimating BMI and the
proportion of participants with elevated BMI.
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