The validity of performance assessment depends to a large extent on the rating scale that is used in the
assessment procedure. It delineates the theoretical construct being measured and yield considerable
influence on how performances are judged and interpreted. Implications of the use of rating scales are
therefore far too important to be taken lightly, particularly in high-stakes standardized tests. This study
investigates the factorial validity and invariance of a writing rating scale used in such a test – the
Malaysian University English Test – in terms of its correspondence to empirical data and the theoretical
construct of ESL writing through the use of confirmatory factor analysis (CFA). To test for factorial
validity, a measurement model was developed based on the construct definition of the MUET rating scale
and tested using AMOS, a data-fitting programme
