EVALUATION OF PARAMETER ESTIMATION METHODS FOR DETERMINATION OF COVARIANCE STRUCTURE IN REPEATED DATA WITH EQUAL AND UNEQUAL TIME INTERVALS


Bati C. T. , Ser G.

FRESENIUS ENVIRONMENTAL BULLETIN, vol.27, no.3, pp.1716-1725, 2018 (SCI-Expanded) identifier

  • Publication Type: Article / Article
  • Volume: 27 Issue: 3
  • Publication Date: 2018
  • Journal Name: FRESENIUS ENVIRONMENTAL BULLETIN
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED)
  • Page Numbers: pp.1716-1725
  • Van Yüzüncü Yıl University Affiliated: Yes

Abstract

This study was completed with the aim of researching the effect of repeated measurement data with equal and unequal time intervals on the selection of the covariance structure and the parameter estimation methods of maximum likelihood (ML) and restricted maximum likelihood (REML). With this aim, blood glucose values took from the tail vein of 63 healthy rats administered plant extracts at varying rates over 21 days were used. Accordingly, while the most appropriate covariance structure was determined as Factor Analitic (FA(1)) for the data set at equal time intervals, the most appropriate covariance structure was determined as ANTE (1) for the dataset with unequal time intervals. There was no apparent difference difference determined for the performance of the parameter estimation methods of ML and REML for both data sets.