Examining the predictive value of combining the theory of planned behaviour and the volunteer functions inventory

The research investigated whether a stronger predictive model of volunteering behaviour prevails when the functions of the volunteer functions inventory are combined with the constructs of the theory of planned behaviour. The study advances on prior research which either examined the predictive capacity of each model or compared their explanatory values. The survey was completed by 186 individuals (Male = 56.10%; Mean Age = 63.7 years) who were retired or approaching retirement and within the context of episodic, skilled volunteering. Multiple regression analyses found that the functions of the volunteer functions inventory explained a further 7% of variability in individuals' willingness to volunteer, over and above that accounted for by the theory of planned behaviour. Within the final model, which explained 62% of variability in willingness to volunteer, significant predictors included attitudes, subjective norms and perceived behavioural control (from the theory of planned behaviour) and the understanding function from the volunteer functions inventory. Items representing the understanding function are proposed to represent a deeper psychological construct (e.g., self-actualisation) not accounted for by the theory of planned behaviour. The findings highlight the potential benefit to be gained from the amalgamation of these two prominent models in terms of improving understanding of volunteerism and providing a single parsimonious model for use in research and practice. Extending the research to include a broader range of volunteering contexts and populations will validate the benefit of combining the models.