BACKGROUND: This study investigates the influence of different variables from the theory of planned behavior (TPB) on intention within multiple donation categories, covering the entire range of lifetime number of donations (LND). Does the same set of variables predict intention equally strong throughout the donor career?
STUDY DESIGN AND METHODS: Measures of intention, self-efficacy, cognitive and affective attitude, and subjective and moral norms were assessed within a sample of 11,480 whole blood donors. Donors were categorized into 65 donation classes using their LND; for example, all donors with one donation (n = 483) in the first donation class, all donors with two donations (n = 447) in the second donation class, and so on. For each donation class, separately for men and women, linear multiple regression models for intention were fitted using self-efficacy, cognitive attitude, affective attitude, subjective norm, and moral norm as predictor variables.
RESULTS: During all stages of the donor career, self-efficacy is the main predictor of intention, with a relatively constant beta (β = 0.64, p < 0.001). Cognitive attitude (β = 0.11, p < 0.001) and moral norm (β = 0.10, p < 0.001) contributed marginally to the prediction. Several sex effects were observed; self-efficacy is a stronger predictor of intention in women, whereas subjective norm predicts intention in men only.
CONCLUSION: Regardless of the number of lifetime donations, the same set of TPB variables, both in composition and in relative strength, predicts intention. A feeling of self-efficacy remains equally important for all donors. It is worthwhile to study whether directed intervention strategies are necessary to target self-efficacy within donor groups with different levels of donation experience.