Exploring the scalar equivalence of the picture vocabulary scale of the Woodcock Munoz language survey across rural and urban isiXhosa-speaking learners
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The fall of apartheid and the rise of democracy have brought assessment issues in multicultural societies to the forefront in South Africa. The rise of multicultural assessment demands the development of tests that are culturally relevant to enhance fair testing practices, and issues of bias and equivalence of tests become increasingly important. This study forms part of a larger project titled the Additive Bilingual Education Project (ABLE). The Woodcock Munoz Language Survey (WMLS) was specifically selected to evaluate the language aims in the project, and was adapted from English to isiXhosa. Previous research has indicated that one of the scales in the adapted isiXhosa version of the WMLS, namely the Picture Vocabulary Scale (PV), displays some item bias, or differential item functioning (DIF), across rural and urban isiXhosa learners. Research has also indicated that differences in dialects can have an impact on test takers’ scores. It is therefore essential to explore the structural equivalence of the adapted isiXhosa version of the WMLS on the PV scale across rural and urban isiXhosa learners, and to ascertain whether DIF is affecting the extent to which the same construct is measured across both groups. The results contribute to establishing the scalar equivalence of the adapted isiXhosa version of the WMLS across rural and urban isiXhosa-speaking learners. Secondary Data Analysis (SDA) was employed because this allowed the researcher to re-analyse the existing data in order to further evaluate construct equivalence. The sample of the larger study consisted of 260 learners, both male and female, selected from a population of Grade 6 and 7 learners attending schools in the Eastern Cape. The data was analysed by using the statistical programme Comprehensive Exploratory Factor Analysis (CEFA) and the Statistical Package for Social Sciences (SPSS). Exploratory factor analysis and the Tucker’s phi coefficient were used. The results indicated distinct factor loadings for both groups, but slight differences were observed which raised concerns about construct equivalence. Scatter plots were employed to investigate further, which also gave cause for concern. It was therefore concluded that construct equivalence was only partially attained. In addition, the Cronbach’s Alpha per factor was calculated, showing that internal consistency was displayed only for Factor 1 and not for Factor 2 for the rural group, or both factors for the urban group. Scalar equivalence across the two groups must therefore be explored further.