BIAS AND LIMITS OF AGREEMENT BETWEEN HYDRODENSITOMETRY, BIOELECTRICAL-IMPEDANCE AND SKINFOLD CALIPERS MEASURES OF PERCENTAGE BODY-FAT

Previous research has often used correlations as a statistical method to show agreement; however, this is not a valid use of the statistic. The purpose of this study was to investigate the bias and limits of ag reement for three methods of estimating percentage body fat for 117 ma le and 114 female university athletes: hydrodensitometry (HYD), bioele ctrical impedance (BIA) and skinfold calipers (SKF). The mean (SD) per centage body fat for males as assessed by HYD, BIA and SKF methods, re spectively, were 13.2 (3.3)%, 14.1 (3.3)% and 13.0 (3.2)%. Female body fat measurements were 22.5 (3.9)%, 23.7 (4.3)% and 23.8 (4.2)%, respe ctively. Pearson product moment correlations for male and female body fat percentages between the three methods were high, ranging from 0.81 to 0.86 (P < 0.05). However, compared to the criterion measure of bod y fat percentage (HYD), the magnitude of agreement BIA and SKF reveale d a different pattern. The mean absolute difference between HYD and BI A measurements of body fat for males was -0.8 (2.0)% fat, and between HYD and SKF was it was 0.2 (1.7)% fat. The mean absolute difference fo r females between HYD and BIA was -1.2 (2.5)%; for HYD and SKF it was -1.4 (2.2)%. Compared to the HYD measures for males and females, the B IA and SKF measures were as much as a 3.8% underestimation and a 6.2% overestimation of body fat. This study provides evidence that the stre ngth of a correlation does not indicate agreement between two methods. In future, reliability and validity studies should examine the absolu te differences between two variables and calculate limits of agreement around which a practitioner can appreciate the precision of the metho dologies.