Inhibitors and facilitators of willingness to participate (WTP) in an HIV vaccine trial: construction and initial validation of the Inhibitors and Facilitators of Willingness to Participate Scale (WPS) among women at risk for HIV infection.

A psychometric scale assessing inhibitors and facilitators of willingness to participate (WTP) in an HIV vaccine trial has not yet been developed. This study aimed to construct and derive the exploratory factor structure of such a scale. The 35-item Inhibitors and Facilitators of Willingness to Participate Scale (WPS) was developed and administered to a convenience sample of 264 Black females between the ages of 16 and 49 years living in an urban-informal settlement near Cape Town. The subscales of the WPS demonstrated good internal consistency with Cronbach's alpha coefficients ranging between 0.69 and 0.82. A principal components exploratory factor analysis revealed the presence of five latent factors. The factors, which accounted for 45.93% of the variance in WTP, were (1) personal costs, (2) safety and convenience, (3) stigmatisation, (4) personal gains and (5) social approval and trust. Against the backdrop of the study limitations, these results provide initial support for the reliability and construct validity of the WPS among the most eligible trial participants in the Western Cape of South Africa.