Accuracy of self-reported weight, height and BMI in US firefighters

Background: Obesity is of increasing concern especially among firefighters. Bias in self-reported body weight, height and body mass index (BMI) has received a great deal of attention given its importance in epidemiological field research on obesity.

Aims: To determine the validity of self-reported weight, height and BMI and identify potential sources of bias in a national sample of US firefighters.

Methods: Self-reported and measured weight and height (and BMI derived from them) were assessed in a national sample of 1001 career male firefighters in the USA and errors in self-reported data were determined.

Results: There were 1001 participants. Self-reported weight, height and BMI were significantly correlated with their respective measured counterparts, i.e. measured weight (r = 0.990; P < 0.001), height (r = 0.961; P < 0.001) and BMI (r = 0.976; P < 0.001). The overall mean difference and standard deviation between self-reported weight, height and BMI were 1.3±2.0kg, 0.94±1.9cm and 0.09±0.9kg/m(2), respectively, for male firefighters. BMI-based weight status (P < 0.001) was the most consistent factor associated with bias in self-reported BMI, weight and height, with heavier firefighters more likely to underestimate their weight and overestimate their height, resulting in underestimated BMIs. Therefore, using self-reported BMI would have resulted in overestimating the prevalence of obesity (BMI ≥ 30.0) by 1.8%, but underestimating the prevalence of more serious levels of obesity (Class II and III) by 1.2%.

Conclusions: Self-reported weight and height (and the resulting BMI) were highly correlated with measured values. A primary and consistent source of error in self-reported weight, height and BMI based on those indices was BMI-based weight status.