To investigate validity of waist circumference measurements obtained by self-report and self-measurement with non-verbal pictorial instructions among a multi-ethnic population.Methods
Five hundred and twenty-six individuals aged 40–75 years (91 South Asian, 430 White European and five other), who attended a screening programme for Type 2 diabetes, estimated their waist circumference and measured their waist with a paper tape measure. Participants were also provided with simple pictorial instructions for measurement of waist circumference in their preferred language and remeasured their waist circumference. We calculated 95% limits of agreement with measures undertaken by a healthcare professional unaware of prior measures.Results
Mean age was 56.8 years (SD 9.0), mean BMI 30.0 kg/m2 (SD 5.6) and mean waist circumference 98.4 cm (SD 14.1). Seventy-nine per cent had high waist circumference according to International Diabetes Federation criteria. The mean of participants' self-reported value was 6.8 cm lower than the healthcare professional measure (SD 8.8; 95% limits of agreement −10.4 to 24.0 cm), with significant differences by sex and ethnicity (South Asian men 7.5 cm, South Asian women 0.1 cm, White European men 7.8 cm, White European women 7.0 cm, P < 0.001). Compared with healthcare professional measures, mean self-measured waist circumference was very similar, both with instructions (0.4 cm higher; SD 5.5 cm; −11.1 to 10.4 cm) and without instructions (0.5 cm lower; SD 5.6; −10.4 to 11.4 cm), but with significant differences by sex and ethnicity (P < 0.001).Conclusions
There was systematic underestimation of self-reported waist circumference in this multi-ethnic UK population. The magnitude of underestimation might reduce the performance of risk scores; however, this can be corrected through self-measurement with pictorial instructions.