Background: Body mass index is used to measure obesity in individuals and to monitor trends in population obesity. Some observers use self-reported height and weight to assess body mass index; others use measured parameters. This paper reports on a study to compare body mass index when calculated from self-reported and measured heights and weights.
Methods: A randomized postal questionnaire survey and follow-up clinical measurement study were carried out in a geographically defined population in the rural South West of England; subjects were 6000 residents of Somerset health district aged 16-64 years selected from the Family Health Services Authority register.
Results: The response rate for the postal questionnaire was 57.6 per cent. A total of 73.3 per cent of responders agreed to clinical measurements; 84 per cent of measured volunteers had over-reported their height and 74 per cent under-reported their weight. The difference between body mass indices based on self-reported and measured values of height and weight is highly statistically significant for the whole population and for most age-sex and body mass groups.
Conclusions: Self-reported heights and weights are unreliable and if used for monitoring health targets should be treated with caution.