title: Reliability studies can be designed more efficiently by using variance components estimates from different sources.
abstract: OBJECTIVE
  Reliability studies are frequently organized within the context of a large (multicenter) study, with only a small sample of subjects measured by the observers of the large study. To estimate interobserver reliability, data from the large study are not frequently used. In this article, the advantages of combining data from the reliability study and the large study to improve the estimation of intra-class correlation coefficients (ICCs) are highlighted.
  
  
  METHODS
  This was done within the scope of estimating fat percentages in the Project On Preterm and Small-for-gestational-age infants-19 (POPS-19) study and with simulations. To calculate ICCs, three approaches were used: (1) the classical approach using data from a reliability study only, (2) the combined variances approach using inter-subject variances from the POPS-19 study, and (3) the maximum likelihood approach using all data.
  
  
  RESULTS
  The ICCs (95% confidence interval [CI]) for fat percentage calculated by the three approaches were 0.84 (0.57, 0.99), 0.94 (0.90, 0.97), and 0.94 (0.88, 0.97), respectively.
  
  
  CONCLUSIONS
  The efficient use of data by combining data from a small reliability study with the data from the large study itself for the calculation of ICCs will lead to more precise ICCs.
authors: Department of Clinical Epidemiology, Leiden University Medical Center, Albinusdreef 2, P.O.Box 9600, 2300 RC Leiden, The Netherlands.
authors: Anne M
authors: AM
authors: Euser
authors: Saskia
authors: S
authors: le Cessie
authors: Martijn J J
authors: MJ
authors: Finken
authors: Jan M
authors: JM
authors: Wit
authors: Friedo W
authors: FW
authors: Dekker
mesh_terms: D000328:Adult; D003627:Data Interpretation, Statistical; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D007234:Infant, Premature; D007236:Infant, Small for Gestational Age; D008297:Male; D015337:Multicenter Studies as Topic / Q000379:methods*; D015588:Observer Variation; D015203:Reproducibility of Results; D012107:Research Design; D012885:Skinfold Thickness