Three studies tested the contribution of perceived autonomy support to the prediction of health-related intentions within the theory of planned behavior. Perceived autonomy support refers to the extent to which individuals perceive that significant others encourage choice and participation in decisionmaking, provide a meaningful rationale, minimize pressure, and acknowledge the individual's feelings and perspectives. Findings from Studies 1 and 2 demonstrated that perceived autonomy support predicted intentions to participate in physical activity behavior directly and indirectly via attitudes. Perceived autonomy support predicted intention even after statistically controlling for the effects from past behavior, descriptive norms, and perceived social support. Study 3 found that persuasive communications influenced perceptions of autonomy support, attitudes, and intentions. Overall, the findings support the incorporation of perceived autonomy support into the theory of planned behavior. Copyright # 2006 John Wiley & Sons, Ltd. Despite the considerable amount of research aimed at understanding the low levels of adherence to health behaviors, social psychologists confess to having limited knowledge of the mechanisms responsible for compliance (Haynes, McDonald, Garg, & Montague, 2003). Thus, there is still a need for theoretically guided research that furthers researchers' and practitioners' grasp of the nature of adherence to health behaviors. The theory of planned behavior is a social cognitive model of decision-making that provides a useful framework for predicting and explaining health behavior (Ajzen, 1991).
THEORY OF PLANNED BEHAVIORAccording to the theory of planned behavior, optimal prediction of behavior can be attained from a person's intention, which is an indicator of how hard people are willing to try, and how much effort European Journal of Social Psychology Eur. J. Soc. Psychol. 37, 934-954 (2007) people plan to exert toward performance of behavior (Ajzen, 1991). Intention is in turn function of attitudes (a person's positive or negative evaluation of performing the behavior), subjective norms (an individual's belief that significant others may exert pressure on them to execute the behavior), and perceived behavioral control (the extent to which people believe that they can control performance of social behavior). According to Ajzen, the construct of perceived behavioral control can also predict behavior directly when behavior is not under complete volitional control and when perceived behavioral control is accurate in a sense that it reflects actual control. Assumptions underlying the theory of planned behavior have been corroborated by numerous meta-analytic reviews across a number of different social behaviors (Armitage & Conner, 2001) and health behaviors (Hagger, Chatzisarantis, & Biddle, 2002). Indeed, tests of the theory of planned behavior have provided strong evidence for the overall predictive validity of intentions, and have shown that attitudes and perceived behavioral contr...