Willingness to participate in an HIV vaccine trial : construction and initial validation of the Willingness to Participate Scale (WTPS), and an application and extension of the Theory of Planned Behavior

[摘要] ENGLISH ABSTRACT: BackgroundSouth Africa is the country with the largest number of HIV infections in the world. As behaviour change initiatives have been suboptimal in curbing the spread of the pandemic, an HIV vaccine is likely to be an important development as a biological agent may circumvent some of the challenges of initiating widespread behaviour change. The development of an HIV vaccine will require several thousands of HIV negative participants who are at high risk of HIV infection to participate in HIV vaccine clinical trials. Before recruitment for such trials may begin, various scientific, ethical, and sociobehavioural issues need to be considered. One of the key sociobehavioural issues concerns the willingness of individuals at high risk of HIV infection to participate in HIV vaccine trials. However, a psychometric measure of willingness to participate (WTP) has not been constructed, and there is a paucity of theory to guide studies of WTP.ObjectivesThe first objective of this study was to construct a psychometric measure of WTP in an HIV vaccine trial, and to derive the exploratory factor structure of the measure. The second objective was to examine the extent to which the Theory of Planned Behavior (TPB) could predict variance in WTP, and to determine whether the TPB was strengthened by the inclusion of mistrust of researchers, knowledge of HIV vaccines and HIV vaccine trials, altruism, and perceived risk of HIV infection as additional predictor variables.MethodologyThis study was a research survey with a cross-sectional design. A convenience sample of 399 participants was recruited from an urban-informal settlement near Cape Town. As 79 of the questionnaires were poorly completed, the final sample size was 320. To develop a measure of WTP in an HIV vaccine trial, an item pool was developed whereby items directly reflected inhibitors and facilitators of WTP. After an iterative process of refinement, the final scale consisted of 35 items and was named the Willingness to Participate Scale (WTPS). A principal component Kaiser normalised exploratory factor analysis (EFA) was conducted on the items that constituted the WTPS. This procedure was performed to identify latent factors which were informed by the items of the scale. To test the predictive capacity of the TPB and the additional predictor variables, a two-step linear hierarchical multiple regression analysis was performed. At step 1, the TPB variables were entered simultaneously. At step 2, the TPB variables along with the additional predictor variables were entered simultaneously.ResultsThe WTPS demonstrated excellent internal consistency (α = 0.90) and initial construct validity, as evidenced by the presence of seven latent factors. The factors accounted for 53.15% of the variance in WTP and were: (i) Social approval and trust; (ii) Stigmatisation; (iii) Personal costs; (iv) Personal gains; (v) Personal risks; (vi) Convenience; and (vii) Safety. The TPB significantly accounted for 6.4% (R² = 0.06) of the variance in WTP [F(3, 316) = 7.16, p < 0.001], yielding a small effect size (ƒ2 = 0.06). The TPB, together with mistrust, knowledge of HIV vaccines and HIV vaccine trials, altruism, and perceived risk of HIV infection as additional predictor variables significantly accounted for 10.2% (R² = 0.10) of the variance in WTP [F(7, 312) = 5.06, p < 0.001], yielding a small to medium effect size (ƒ2 = 0.11). Subjective norms, mistrust of researchers, altruism, and perceived risk of HIV infection were significant independent predictors of WTP.ConclusionAgainst the backdrop of the study limitations, the results of this study provide initial support for the reliability and construct validity of the WTPS among the most eligible trial participants in the Western Cape of South Africa. The findings also suggest that the TPB may not be an appropriate theoretical framework for predicting WTP in an HIV vaccine trial in this context. Nonetheless, normative pressure by others, mistrust of researchers, altruism, and perceived risk of HIV infection may influence WTP in this population. Implications for future research are discussed.

[发布机构] Stellenbosch University