Digitized using a Konica Minolta 211 PCL Scanner. 300dpi (OCR). / Thesis (MA (Psychology))--University of Stellenbosch, 2007. / ENGLISH ABSTRACT: The first objective of the present study was to determine whether the Theory of Planned Behaviour (TPB) could predict Willingness to Participate (WTP) in a future Phase III HIV vaccine trial among high risk adolescents in the Western Cape. The second objective was to determine whether the additional predictor variables of Self perceived risk of HIV infection, Knowledge of HIV vaccines and HIV vaccine trials, Attitudes toward HIV I AIDS and Health-promoting behaviours could further explain WTP in a future Phase III HIV vaccine trial among adolescents. A convenience sample of 224 adolescents attending secondary schools located in an African township on the Cape Flats was recruited for the present study. Hierarchical logistic regression analyses indicated that the TPB significantly improved the prediction of WTP in an HIV vaccine trial. Prediction success was 79.9%. Of all the predictor variables, only Subjective norms significantly predicted WTP in an HIV vaccine trial (OR = 1.19,95% C.L = 1.06-1.34). A second stepwise logistic regression analysis showed that Subjective norms (OR = 1.19, 95% c.I. = l.07-1.34) and Attitude towards participation in an HIV vaccine trial (OR = 1.32,95% C.L = 1.00-1.74) were significant predictors of WTP in an HIV vaccine trial. Prediction success was 80.4%. These findings provide support for the Theory of Reasoned Action (TRA) and suggest that psychosocial factors may play a role in WTP in a future Phase III HIV vaccine trial among adolescents. HIV vaccine trial preparedness programs targeting adolescents should aim to influence group norms positively and promote positive attitudes toward participation in a future Phase III HIV vaccine trial. / AFRIKAANSE OPSOMMING: Die eerste oogmerk van die huidige studie was om te bepaal of die teorie van beplande gedrag (TBG) die bereidwilligheid tot deelname (BTD) aan 'n toekomstige fase III-MIV-entstofproefneming onder hoe risiko adolessente in die Wes-Kaap kan voorspel. Die tweede oogmerk was om te bepaal of die bykomende voorspellingveranderlikes, naamlik selfwaargenome risiko vir MIV -besmetting, kennis van MIV -entstowwe en MIV -entstofproefnemings, houdings jeens MIV /Vigs en gesondheidsbevorderende gedrag BTD in 'n toekomstige fase III-MIV entstofproefneming kan verduidelik. 'n Geriefsmonster van 224 adolessente wat sekondere skole gelee in 'n dorpsgebied in Kaapstad, bywoon, is vir die huidige studie gewerf. Hierargiese logistiese regressie-analises toon dat die TBG die voorspelling van BTD aan 'n MIV -entstofproefneming aanmerklik verbeter het. Voorspellingsukses was 79.9%. Van al die voorspellingveranderlikes het slegs subjektiewe norme BTD aan 'n MIV -entstofproefneming beduidend voorspel (RK = 1.19, 95% VI = 1.06-1.34). 'n Tweede stapsgewyse logistiese regressie-analise toon dat subjektiewe norme (RK = 1.19, 95% VI = 1.07-1.34) en houding jeens deelname aan 'n MIV-entstofproefneming (RK = 1.32,95% VI = 1.00-1.74) beduidende voorspellers van BTD aan 'n MIV -entstofproefneming was. Voorspellingsukses was 80.4%. Hierdie bevindinge verleen steun aan die teorie van beredeneerde aksie (TBA) en doen aan die hand dat psigososiale faktore moontlik in die toekoms 'n rol in BTD aan 'n fase Ill-MIV-entstofproefneming onder adolessente kan speel. Programme wat op adolessente se gereedheid vir entstofproefnemings afgestem is, behoort te poog om groepnormne positief te beinvloed en positiewe houdings jeens deelname aan 'n toekomstige fase III -MIV -entstofproefneming te bevorder.