An Investigation into the Dimensional Structure of ESL Academic Writing Skills on TOEFL iBT Independent Essays

Abstract

This two-phase study examines the ways in which the construct of ESL academic writing is dimensionally determined on Test of English as a Foreign LanguageTM Internet-based test (TOEFL® iBT) independent essays, using both substantive and statistical methods. In the first phase, four ESL academic writing experts sorted 35 descriptors of ESL academic writing into dimensionally distinct ESL writing skills. In the second phase, a series of conditional covariance-based nonparametric dimensionality tests were conducted using the ratings awarded by 10 ESL teachers on 480 TOEFL iBT independent essays. The results from both substantive and statistical analyses indicated that (a) five writing skills (content fulfillment, organizational effectiveness, grammatical knowledge, vocabulary use, and mechanics) represent the construct of the TOEFL iBT independent writing; (b) each of the five writing skills is a statistically significant distinct dimension; and (c) writing skills associated with content fulfillment and organizational effectiveness are dimensionally different from those related to grammatical knowledge, vocabulary use, and mechanics. These findings are used as the basis for a discussion of the need for an analytic scoring system and diagnostic assessment in ESL academic writing.