Sample Size for Estimation of G and Phi Coefficients in Generalizability Theory

Atilgan H.

EURASIAN JOURNAL OF EDUCATIONAL RESEARCH, vol.13, no.51, pp.215-227, 2013 (Journal Indexed in SSCI) identifier identifier

  • Publication Type: Article / Article
  • Volume: 13 Issue: 51
  • Publication Date: 2013
  • Page Numbers: pp.215-227
  • Keywords: Generalizability theory, sample size, generalizability coefficient, Phi coefficient, RELIABILITY


Problem Statement: Reliability, which refers to the degree to which measurement results are free from measurement errors, as well as its estimation, is an important issue in psychometrics. Several methods for estimating reliability have been suggested by various theories in the field of psychometrics. One of these theories is the generalizability theory. In generalizability theory, two distinct reliability coefficients are estimated: the generalizability coefficient (G coefficient) for relative evaluation, and the index of dependability (Phi coefficient) for absolute decisions. Like in all methods of reliability estimation, G and Phi coefficients are estimated based on a data set obtained from a sample as a result of administering the instrument. Therefore, it has been a critical issue to determine what sample size is necessary in order to reliably estimate the population's characteristics.