Predicting future blood donor returns: past behavior, intentions, and observer effects.

A prospective design was used to explore the efficacy of 6 factors (e.g., intentions) to predict the number of future blood donations in an initial sample of 630 blood donors. Differential predictions are made for the roles of past behavior and intentions with respect to occasional (4 or fewer previous blood donations) and regular (5 or more previous blood donations) blood donors. Intentions were predictive for occasional donors, and past behavior was predictive for regular donors. Furthermore, for regular donors only, an inverted U-shaped curve explained the relationship between past behavior and future behavior. Finally, it is reported that observing others fainting produces a reduction in the number of future donations for occasional donors. The theoretical and practical implications of these findings are discussed.