Cultural biases in the Peabody Picture Vocabulary Test-III: Testing Tamariki in a New Zealand Sample

Abstract

Issues of cultural bias in psychometric assessment have been widely debated in the research literature, with a range of views arising as to the ways in which cultural differences might compromise the validity of psychometric test results (Ogden, 2003; Ogden & McFarlane Nathan, 1997; Shepherd & Leathem, 1999). Despite the continued debate about the effects of cultural bias, most professionals acknowledge that test content and administration procedures are invariably culturally bound, with some tests having a higher cultural loading and potential for bias than others. Test developers acknowledge the need to consider the impact of test content, test materials and test conditions on the reliability and validity of a test in an attempt to minimise the effects of cultural bias. In an unbiased measure, high or low scores reflect attributes of the person being assessed and cannot be seen as artefacts arising from culturally different understandings of the test material (Stockman, 2000). Within a New Zealand context, there is very little research that has investigated the appropriateness of using psychometric tools with Maori and more specifically, Maori tamariki. The Peabody Picture Vocabulary Test (PPVT) is one psychometric tool that was designed and standardised for use with children in the United States, but is used in New Zealand with Maori children both clinically and in research (Phillips et al., 2004; Reese & Read, 2000). A previous version, the PPVT-R was found to produce different results for White American and African American kindergarten aged children (Rock, 2005). The results showed that African American first grade children tested with the PPVT-R obtained scores which suggested that they had approximately half the vocabulary of White American first grade children. The discrepancy between African American and White American children's scores on the PPVT-R remained close to one standard deviation apart, even after controlling for factors such as socio-economic status (SES), parental education, and low birth weight (Rock, 2005). The PPVT-III, which according to test developers was standardised on a representative U.S. sample, is purported to be a culturally valid test due to the inclusion of a large representative group of ethnic minority children within the wider norm group (Dunn & Dunn, 1997; Stockman, 2000). In gauging the suitability of the PPVT-III for use with an at-risk sample of African American children, Washington and Craig (1999) found that their scores on the PPVT-III did not significantly differ from the norm group. As a result of this finding, they concluded that the PPVT-III represents a valid and culturally fair test suitable for use with African American children. However, on review of the available literature, it was apparent that limited research has been conducted in order to systematically investigate the use of the PPVT-III with people from diverse cultural backgrounds. Despite this seemingly well-intentioned move to reduce any previously existing cultural bias, some researchers argue that the mere inclusion of an ethnic minority norm group does not render a test unbiased. In order for a test to be considered unbiased, it must also measure culturally appropriate knowledge and utilise methods of testing suitable for people from different cultural backgrounds (Palmer, 2004). In New Zealand a number of researchers have made use of the PPVT-III as a measure of verbal knowledge and receptive vocabulary development in children (Phillips et al., 2004; Reese & Cox, 1999; Reese & Read, 2000). Although not standardised for use in New Zealand, the PPVT-III was chosen as a research tool because of its widespread usage in similar studies and its position as a well known test of emergent language (Phillips et al., 2004). Reese and Read (2004) measured the reliability of the PPVT-III for use amongst a mixed ethnicity sample of New Zealand children and found that the test-retest reliability of the PPVT-III closely matched that reported by the American norm reference group. …

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