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

Fincham, Dylan Shaun (2008-12)

Thesis (PhD)--Stellenbosch University, 2008.

Thesis

ENGLISH ABSTRACT: Background South 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. Objectives The 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. Methodology This 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. Results The 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. Conclusion Against 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.

AFRIKAANSE OPSOMMING: Agtergrond Suid afrika is die land met die hoogste getal HIV infeksies in die wêreld. Vir die ontwikkeling van 'n HIV entstof, sal daar vereis word dat duisende HIV negatiewe deelnemers, wat 'n hoë risko kans staan om HIV infeksie op te doen, moet deelneem aan 'n kliniese HIV vaksine proeftog. Verskeie, wetenskaplike, etiese en sosiale gedrags punte moet oorweeg word, voor die werwing van sulke proefnemings. Een van die hoof aspekte van sosiale gedrags punte is die bereidwillgheid van 'n individu om blootgestel te word aan die HIV infeksie tydens die proeftog. 'n Psigometriese skatting van bereidwiligheid om deel te neem (BODTN) is egter nog nie gekonstruktureer nie en daar is 'n skaarste/geringheid in studies om as gids te dien vir die BODTN. Doel Die eerste doel van hierdie studie was om 'n psigometriese skatting van BODTN in ’n HIV vaksiene proefneming te konstruktureer, en om die ondersoekings oorsaak/faktor struktuur daarvan te meet en af te lei. Die tweede doel was om ondersoek in te stel of die omvang van die Teorie van Beplande Gedrag (TBG) verskille kan voorspel in die BODTN, en om vas te stel of die TBG versterk word deur die insluiting van wantroue in navorsers, kennis van HIV vaksienes en HIV vaksiene proefnemings, altruïsme, en die begrypbare risko van HIV infeksie as adisionele voorspellers. Metode Hierdie studie is 'n navorsings ondersoek met 'n deursneeproef ontwerp. ’n Grieflike aantal van 399 deelnemers was gewerf van 'n informele nedersetting naby Kaapstad. Die finale getal was 320 omdat 79 nie die vraelys korrek on volledig ingevul het nie. Na 'n interaktiewe proses van suiwering/verfyning, het die finale skaal uit 35 items bestaan en word die skaal benoem na die Willingness to Participate Scale (WTPS). Die prinsipale komponent Kaiser normaliseer EFA wat gedoen was op die items wat die WTPS konstitueer. Hierdie prosedure was gedoen om die latente faktore te identifiseer wat beskikbaar gestel was deur die items van die skaal. Om die voorspelbare kapasiteit van die TBG en die adisionele voorspelbare verskille te toets, het ons 'n twee stap hiërargiese veelvoudige agteruitgaan analise gebruik. By stap 1 was die TBG veranderlikes gelyktydig ingedruk. By stap 2 is die TBG veranderlikes tesame met die adisionele voorspellers in gedruk. Resultate Die WTPS het uitstekende interne konsistensie en 'n aanvanklike geldigheid gedemonstreer, soos bewys deur die teenwoordigheid van die 7 latente faktore. Die faktore verantwoord 53.15% van die verskil in WTP en was: (i) Sosiale aanvaarding en vertroue; (ii) Stigma; (iii) Persoonlike koste; (iv) Persoonlike wins/profyt; (v) Persoonlike risiko's; (vi) Gerieflikheid; en (vii) Veiligheid. Die TBG verantwoord 6.4% (R²=0.06) van die verskil in BODTN [F(3.316) = 7.16, p<0.001] met 'n toegewende klein groote uitwerking/uitslag. Die TBG tesame met wantroue, kennis van HIV vaksienes en HIV vaksiene proefnemings, altruïsme, en begrypbare risko van HIV infeksie as adisionele voorspellers, verwantwoord 10.2% (R²=0.10) van die verskil in BODTN [F(7.312 = 5.06, p<0.001], met 'n toegewende klein tot medium groote uitwerking/uitslag (f²=0.11). Subjektiewe norme, wantroue in navorsers, altruïsme, en 'n beprypbare risko van HIV infeksie was betekenisvolle, onafhanklike voorspellers van die BODTN. Gevolgtrekking Teen die agtergrond van die studie beperkinge, het die resultate van hierdie studie ondersteuning voorsien aan die vertroubaarheid en konstruktiewe geldigheid van die WTPS onder die mees geskikste proef deelnemers in die Wes Kaap van Suid Afrika. Die bevinding stel ook voor dat die TBG nie altyd 'n geskikte teoretiese raamwerk is vir die voorspelling van die BODTN in 'n HIV vaksiene proefneming in hierdie konteks is nie. Des nie teen staande, normale druk van ander, wanrtroue in navorsers, altruïsme en die begrypbare infeksie van HIV kan die populasie deur die BODTN beinvloed word. Implikasies vir toekomstige navorsing is bespreek.

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