Investigating item and construct bias in an English verbal analogies scale

DOI: 10.2989/16073614.2012.739407
Author(s): Ghouwa IsmailMedical Research Council, South Africa, Elize KochResearch Associate, South Africa


For this study the researcher was interested in investigating the scalar equivalence of the adapted English version of the verbal analogies (VA) subscale of the Woodcock Muñoz Language Survey (WMLS) across English first-language speakers and Xhosa first-language speakers. This was achieved by utilising differential item functioning (DIF) and construct bias statistical techniques. The Mantel-Haenszel DIF detection method was employed to detect DIF, while construct equivalence was examined by means of exploratory factor analysis (EFA) utilising an a priori two-factor structure. The Tucker's phi coefficient was used to assess the congruence of the construct across the two language groups. The sample consisted of 192 English and 193 Xhosa first-language learners, who were selected from ex-Model C and previously disadvantaged schools in the Port Elizabeth and Grahamstown region. The main findings of this study indicated that the adapted English version of the VA scale displayed DIF items across the two language groups. Moreover, construct equivalence could only be established for one factor across the two language groups, as the second factor displayed non-negligible incongruities even after the removal of DIF items.

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