ESTIMATES OF THE SOURCES OF VARIATION (VARIANCE-COMPONENTS) OF BIOELECTRIC IMPEDANCE AND ANTHROPOMETRIC MEASUREMENTS IN AN EPIDEMIOLOGIC CASE-CONTROL STUDY OF BREAST-CANCER

Objective: This study investigated the variability of anthropometric m easurements and body fat estimated by bioelectric impedance analysis. Subsequently the methods were applied in a case-control study to inves tigate the association with breast cancer. Design, Subjects: The study group included 50 consecutive cases and 75 age-matched controls from the same area The variation was investigated in 50 healthy women from the control group, who were repeatably measured using standardised mea surement procedures, and the variation between-subjects, within-subjec ts, between-observers, and within-observers were estimated. Results, C onclusions: The study showed that the variance components between-subj ects were 64-99% of the total variance. The variables of skinfold thic knesses were characterised by having the highest relative observer var iation and having many unavailable values that were out of the range o f the Harpenden callipers. The mean body fat by bioelectric impedance analysis was 31.2%, and the total coefficient of variation 23%, while the variance components related to subject time, observer and measurem ent were 98.4%, 1.1%, 0.2%, and 0.4%, respectively. The body fat was s ignificantly correlated with the variables of skinfold thicknesses. We decided to exclude the variables of skinfold thicknesses from the cas e-control study, and for the other variables to measure each subject o nly at one time by one observer. The case-control part of the study in dicated a non-significant increase in body weight in the postmenopausa l breast cancer patients (mean difference 3.6 kg; confidence interval from -0.9 kg to 8.0 kg). Similarly the body fat tended to be higher in the breast cancer patients (mean difference 1.2%; confidence interval from -1.6% to 4.0%).