An investigation into the dimensionality of TOEFL using conditional covariance-based nonparametric approach

This article reports two studies to illustrate methodologies for conducting a conditional covariance-based nonparametric dimensionality assessment using data from two forms of the Test of English as a Foreign Language (TOEFL). Study I illustrates how to assess overall dimensionality of the TOEFL including all three subtests. Study 2 is aimed at illustrating how to conduct dimensionality analyses for a testlet-based test by focusing on the Reading Comprehension (RC) section in combination with item content analyses and hypothesis testing. The results of Study I indicated that both TOEFL forms involve two dominant dimensions corresponding to the Listening Comprehension section and the combination of the Reading Comprehension section and Structure and Written Expression section. The extensive RC analyses from Study 2 revealed strong evidence that a significant amount of the RC multidimensionality came from testlet effects. Confirmatory analyses coupled with exploratory cluster analyses and substantive item content analyses further identified dimensionality structure having to do with reading subskills.