Accuracy of self-reported height, weight, and waist circumference in a general adult

Background

Self-reported height, weight, and waist circumference (WC) are widely used to estimate the prevalence of obesity, which has been increasing rapidly in China, but there is limited evidence for the accuracy of self-reported data and the determinants of self-report bias among the general adult Chinese population.
Methods

Using a multi-stage cluster sampling method, 8399 residents aged 18 or above were interviewed in the Jiangsu Province of China. Information on self-reported height, weight, and WC, together with information on demographic factors and lifestyle behaviors, were collected through structured face-to-face interviews. Anthropometrics were measured by trained staff according to a standard protocol.
Results

Self-reported height was overreported by a mean of 1.1 cm (95 % confidence interval [CI]: 1.0 to 1.2). Self-reported weight, body mass index (BMI), and WC were underreported by −0.1 kg (95 % CI: −0.2 to 0.0), −0.4 kg/m2 (95 % CI: −0.5 to −0.3) and −1.5 cm (95 % CI: −1.7 to −1.3) respectively. Sex, age group, location, education, weight status, fruit/vegetable intake, and smoking significantly affected the extent of self-report bias. According to the self-reported data, 25.5 % of obese people were misclassified into lower BMI categories and 8.7 % of people with elevated WC were misclassified as normal. Besides the accuracy, the distribution of BMI and WC and their cut-off point standards for obesity of a population affected the proportion of obesity misclassification.

TL:DR

  • BMI = measure of “bigness”
  • Waist Circumference =  measure of abdominal adiposity
  • People tend to under-report weight, BMI and WC.
  • People tend to over-report height
  • ~25% of people who classified themselves as within “normal – overweight” BMI based on self-measurements are actually obese based on the directly measured stats.

Use of BMI

The Body Mass Index (BMI)

  • Recognised that it does not differentiate between the muscular and the overweight, except at very high BMIs
  • Does not distinguish between individuals with different types of fat distribution.

Waist circumference (WC)

  • Measure of abdominal obesity
  • Commonly under reported

Self-report vs Actual

  • People tend to over report height, especially as they get older.
  • People tend to under-report weight, BMI and WC across all age group and income groups
  • Women tend to under-report more than men
  • Obese/overweight = over-report height, under-report weight, BMI and WC
  • “Healthier” people (eg. exercise, non-smokers) tend to over-report height and under-report WC

Misclassification

  • ~25% of people who classified themselves as within “normal – overweight” BMI based on self-measurements are actually obese based on the directly measured stats.
  • increased incidence of misclassification amongst women vs men
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