Video instructions improve accuracy of self-measures of waist circumference compared with written instructions

Objective: To determine whether video-based instructions improve the accuracy of self-measures of waist and hip circumference compared with written instructions. Design: Population-based, cross-sectional study. Self-measurements of waist circumference (WC) and hip circumference (HC) of fifty-seven participants randomly allocated to receive either written instruction or video instruction were compared with those of a trained technician. Setting: Aberdeen, Scotland, and Brussels, Belgium, between February and April 2010. Subjects: Adults aged 18-62 years with a high level of English language and no prior training in anthropometry. Results: WC was significantly overestimated by the written method (1.75 cm bias; P = 0.007) but not the video method (0.95 cm bias; P = 0.239). HC was significantly underestimated in both written (-0.35 cm bias; P = 0.009) and video methods (-0.75 cm bias; P = 0.046). Reliability was not significantly affected by age, sex, BMI or WC. Bland-Altman plots demonstrated wide limits of agreement for WC (-6.83, 6.08 cm for written method; -10.14, 6.72 cm for video method) and HC (-12.85, 1.60 cm for written method; -10.82, 2.50 cm for video method). Conclusions: Video technology can support more accurate self-measurements of anthropometric data in epidemiological studies. Further research is warranted using larger and more heterogeneous samples in order that results can be generalised.