Reliability of anthropometric measurements in overweight and lean subjects:: consequences for correlations between anthropometric and other variables

OBJECTIVE: To estimate the reliability of anthropometric measurements in overweight and lean subjects, and to examine the influence of this reliability on correlations to other variables, since low reliability leads to underestimation of correlations. DESIGN: Replicate measurements by two observers in 26 overweight and 25 lean subjects measured at two occasions. MEASUREMENTS: Sagittal abdominal diameter (SAD), waist circumference (waist), waist-to-hip ratio (W/H) and skinfold measurements. RESULTS: Intra-class correlation coefficients (ICCs) for SAD and waist were higher than for W/H (0.98 vs 0.90, P < 0.001, and 0.97 vs 0.90, P = 0.001, respectively). For waist, the ICC was lower for overweight than for lean subjects (0.85 vs 0.95, P = 0.030), but the ICC values were comparable for SAD and W/H (0.92 vs 0.95 and 0.78 vs 0.83, respectively). Intra-observer variations (IOV) for SAD and waist were lower than for W/H (coefficients of variation; 1.6%, 1.4% and 2.3%, respectively), as were intra-subject Variations (ISV) (2.7%, 3.0% and 3.4%, respectively). ICC values ranged from 0.84 to 0.93 and were lower for overweight than for lean subjects for biceps, subscapular and umbilical skinfolds (P = 0.031, P < 0.001 and P = 0.048, respectively). Coefficients of variations for skinfold measurements ranged between 7.3% and 16.0% for IOV and between 14.9% and 20.8% for ISV. CONCLUSIONS: The low ICC values imply that correlations can be underestimated in overweight groups. We propose that, because of their higher reliability, SAD and waist have a higher predictive capacity for cardiovascular risk than W/H. SAD is the only measurement with high reliability in both weight groups and its use is recommended.