The purpose of this paper is to test whether, in the context of blood donation, the predictive ability of the theory of planned behaviour (TPB) extends from behavioural intention to actual donation behaviour, and whether extended versions of the TPB perform better than the standard version.
Intentions to donate blood predicted by the TPB are compared with an accurate measure of blood donation behaviour obtained following a mobile blood drive by the New Zealand Blood Service.
When the observed outcome is donation behaviour rather than behavioural intention, the TPB model's performance drops. Extending the variables in the model to include moral obligation and past behaviour does not improve its predictive ability, and neither does the use of belief‐based variables.
The TPB is much less effective in predicting blood donation behaviour than it is in predicting intentions to donate blood. But only actual donation behaviour yields medical supplies. This study suggests that to advance the goal of increasing donation rates, attention needs to turn to methods other than the TPB to identify variables that do predict donation behaviour.
The present study gathered one of the largest samples used for TPB blood donation research; this enabled predictions made using the TPB to be tested against actual behaviour, rather than behavioural intention, the measure typically used in blood donation studies. Because blood donation is a low‐incidence behaviour, previous studies have been hampered by small sample sizes, that inevitably contain few donors, and no measure of actual donation behaviour.
