title: Statistical validation of air-displacement plethysmography for body composition assessment in children.
abstract: BACKGROUND
  Body composition assessment of children has been hindered by the absence of a safe, quick, and easily tolerated gold standard technique. Existing validation studies of air-displacement plethysmography (ADP) have been based on small, narrowly defined samples, using simple linear regression or Bland-Altman analyses.
  
  
  OBJECTIVE
  Correlations within a multitrait-multimethod matrix (MTMM) and factor analytic methodologies were used to evaluate ADP as a valid and reliable body composition technique for children.
  
  
  METHODS
  Fat mass (FM), fat-free mass (FFM) and per cent body fat (%BF) were measured in 139 children, 7-10 years old, by ADP, dual energy X-ray absorptiometry (DXA) and anthropometry (ANTH). MTMM and factor analysis were used to compare assessment techniques.
  
  
  RESULTS
  Reliability estimates were lower for ADP than for either ANTH or DXA. Convergent and discriminant correlations between ADP and ANTH or DXA were high for identical as well as non-identical measures. Two body composition factors (Fatness, Leanness) and two technique-related factors (Bod Pod, Anthropometry) were identified.
  
  
  CONCLUSIONS
  ADP offers a valid and reliable means of assessing body composition in children but does not perform as well as ANTH or DXA. MTMM and factor analytic methodologies offer an effective alternative to assessing body composition.
authors: Biostatistics and Data Management Core, University of Pennsylvania School of Medicine, PA 19104, USA. ITTENBACH@email.chop.edu
authors: Richard F
authors: RF
authors: Ittenbach
authors: Anne M
authors: AM
authors: Buison
authors: Virginia A
authors: VA
authors: Stallings
authors: Babette S
authors: BS
authors: Zemel