Differential Item Functioning (DIF) occurs when examinees with the same ability have different probabilities of endorsing an item. Conventional DIF detection methods (e.g., the Mantel-Hansel test) can be used to detect DIF only across observed groups, such as gender or ethnicity. However, research has found that DIF is not typically fully explained by an observed variable (e.g., Cohen & Bolt, 2005). True source of DIF may be unobserved, including variables such as personality, response patterns, or unmeasured background variables. The Factor Mixture Model (FMM) is designed to detect unobserved sources of heterogeneity in factor structures, and an FMM with binary outcomes has recently been used for assessing DIF (DeMars & Lau, 2011; Jackman, 2010). However, FMMs with binary outcomes for detecting DIF have not been thoroughly explored to investigate both types of between-class latent DIF (LDIF) and class-specific observed DIF (ODIF). The present simulation study was designed to investigate whether models correctly specified in terms of LDIF and/or ODIF influence the performance of model fit indices (AIC, BIC, aBIC, and CAIC) and entropy, as compared to models incorrectly specified in terms of either LDIF or ODIF. In addition, the present study examined the recovery of item difficulty parameters and investigated the proportion of replications in which items were correctly or incorrectly identified as displaying DIF, by manipulating DIF effect size and latent class probability. For each simulation condition, two latent classes of 27 item responses were generated to fit a one parameter logistic model with items’ difficulties generated to exhibit DIF across the classes and/or the observed groups. Results showed that FMMs with binary outcomes performed well in terms of fit indices, entropy, DIF detection, and recovery of large DIF effects. When class probabilities were unequal with small DIF effects, performance decreased for fit indices, power, and the recovery of DIF effects compared to equal class probability conditions. Inflated Type I errors were found for invariant DIF items across simulation conditions. When data were generated to fit a model having ODIF but estimated LDIF, specifying LDIF in the model fully captured ODIF effects when DIF effect sizes were large. / text

Magister Psychologiae - MPsych / In many countries defined by multilingualism, language has been identified as a great influence during psychological and educational testing. In South Africa (SA), factors such as changes in policies and social inequalities also influence testing. Literature supports the translation and adaptation of tests used in such contexts in order to avoid bias caused by language. Different language versions of tests then need to be evaluated for equivalence, to ensure that scores across the different language versions have the same meaning. Differences in dialects may also impact on the results of such tests.Results of an isiXhosa version of the Woodcock Muñoz Language Survey (WMLS),which is a test used to measure isiXhosa learners’ language proficiency, show significant mean score differences on the test scores across rural and urban firstlanguage speakers of isiXhosa. These results have indicated a possible problem regarding rural and urban dialects during testing. This thesis evaluates the item bias of the subtests in this version of the WMLS across rural and urban isiXhosa learners. This was accomplished by evaluating the reliability and item characteristics for group differences, and by evaluating differential item functioning across these two groups on the subtests of the WMLS. The sample in this thesis comprised of 260 isiXhosa learners from the Eastern Cape Province in grade 6 and grade 7, both males and females. This sample was collected in two phases: (1) secondary data from 49 rural and 133 urban isiXhosa learners was included in the sample; (2) adding to the secondary data, a primary data collection from 78 rural isiXhosa learners was made to equalise the two sample groups. All ethical considerations were included in this thesis. The results were surprising and unexpected. Two of the subtests in the WMLS showed evidence of scalar equivalence as only a few items were identified as problematic. However, two of the subtests demonstrated more problematic items. These results mean that two subtests of the WMLS that demonstrated evidence of scalar equivalence can be used to measure the construct of language proficiency, while the other two sub-tests that showed problematic items need to be further investigated, as the responses given by learners on these items seem to be determined by their group membership and not by their ability.

The present study examined the factor structure and measurement invariance of the revised version of the Athletic Coping Skills Inventory (ACSI-28), following adjustment of the wording of items such that they were appropriate to assess Coping Skills in an educational setting. A sample of middle school students (n = 1,037) completed the revised inventory. An initial confirmatory factor analysis led to the hypothesis of a better fitting model with two items removed. Reliability of the subscales and the instrument as a whole was acceptable. Items were examined for sex invariance with differential item functioning (DIF) using item response theory, and five items were flagged for significant sex non-invariance. Following removal of these items, comparison of the mean differences between male and female coping scores revealed that there was no significant difference between the two groups. Further examination of the generalizability of the coping construct and the potential transfer of psychosocial skills between athletic and academic settings are warranted.