Measurement scales for AIDS-related knowledge and stigma in South Africa: An evaluation using item response theory

AIDS-related knowledge and stigma are key issues in combatting the HIV/AIDS pandemic, primarily because of their relationship with HIV/AIDS testing behavior. Previous studies exploring these issues in southern Africa have employed the 11-item AIDS-related knowledge scale and the 9-item stigma scale, but there has been limited psychometric testing of these scales. Using Item Response Theory (IRT), the two scales were investigated within the context of construction workers in South Africa. The IRT evaluation of these scales offers advantages over classical test theory (CTT) tests as they permit more nuanced understanding of the performance of individual items. Survey data from 512 construction workers in the Western Cape, South Africa, were used for the evaluation. Based on the tests, a revised 9-item AIDS-related knowledge scale and revised 8-item AIDS-related stigma scale were developed. The slope estimates and threshold parameters for the knowledge scale indicated a robust scale which is most reliable for respondents with low to moderate levels of AIDS knowledge, and less so for those with high knowledge levels. Similar estimates for the stigma scale indicated good reliability at moderate to high levels of AIDS-related stigma, declining when stigma was at low levels. The analysis indicates that the scale items are most precise/reliable when used in populations with (1) lower levels of education, (2) who are more likely to adhere to more traditional or non-scientific beliefs about the origin and causes of HIV and AIDS, and (3) and as a consequence of the first two, who are more likely to exhibit high levels of stigma towards those with HIV/AIDS. The results have various policy and programmatic implications for epidemiological efforts at addressing the pandemic, particularly interventions intended to boost serostatus testing behaviour, such as voluntary counselling and testing (VCT). Greater measurement integrity for applied scales improves the overall rigour of such interventions, thereby ensuring better targeting of high risk populations and more focused allocation and utilization of health financial, technical and human resources, two critically important factors in addressing the pandemic in resource-poor contexts.