Document Type : Original Research Article
Science and Research Branch, Islamic Azad University, Tehran, Iran.
Shahid Beheshti University, Tehran, Iran.
The distinction between psychometric and psychological unidimensionality is a very debatable issue in tests of psychological constructs including language ability tests. In the language testing literature, psychometric unidimensionality has been controversially found not to necessarily guarantee psychological unidimensionality and vice versa. This issue provided impetus for this study to see what the analysis of psychometric unidimensionality of writing reveals about its psychological unidimensionality from an a priori construct validity perspective. In this study, Principal Component Analysis, as a frequently used technique in language testing, was employed to investigate unidimensionality. The results of the analysis on a heterogeneous sample of writings by 135 EFL learners demonstrate that writing is both psychometrically and psychologically unidimensional only in terms of its linguistic rather than mechanical aspects; however, it does not mean that the mechanical aspects of writing should not be considered in assessing writing.