Comparison of segmental and global bioimpedance spectroscopy errors using generalizability theory

The generalizability theory, an expansion of classic true-score reliability theory, was used to investigate the generalizability of observed segmental extracellular fluid (ECF) and intracellular fluid (ICF) distribution measurements. The test instrument was a Xitron Hydra ECF/ICF bioimpedance analysis system model 4200, Xitron Technologies, San Diego, CA. Fifty American healthy men (17-72 years) and 50 American healthy women (17-76 years) volunteered as participants. Xitron continuous segmental ECF-ICF procedures for testing leg segmental data were followed for testing participants in both the standing erect and lying supine postures. A two-facet, person-by-trial, completely crossed design was used. All facets were treated as random. During a one-day session each subject was tested involving 20 trials for the standing erect posture and 20 trials for the lying supine posture. Data on each fluid measurement, each body posture and each sex group were independently analysed. The analyses revealed that the trial factor accounted for less than 0.2% of the total variance for ECF and ICF scores. ECF and ICF generalizability coefficients for the segmental method were 0.99 or greater. In comparing ECF segmental to ECF global, results showed generalizability coefficients were similar. However, ICF segmental coefficients were larger than the coefficients produced by the global method. In conclusion, the segmental method appeared more reliable than the global method, under the conditions of this study.