Functional signi®cance of psychological variables that are included in the Theory of Planned Behaviour: A Self-Determination Theory approach to the study of attitudes, subjective norms, perceptions of control and intentions

The Theory of Planned Behaviour was proposed by Ajzen (1985) in an attempt to expand the applicability of the Theory of Reasoned Action (TRA) to situations where behaviour is not under complete volitional control. However, recent research does not address the issue of the stability of intentions, yet this is considered a boundary condition of the TRA on theoretical grounds. Therefore, the purposes of the present article were, ®rst, to make a theoretical approach to the study of the stability of behavioural intentions by discussing assumptions underlying self-determination theory. Second, because, according to self-determination theory (Deci & Ryan, 1985), stability of intentions is related to the functional signi®cance of psychological events, investigation of the functional signi®cance of attitudes, subjective norms and perceived behavioural control was attempted through a study dealing with leisure-time physical activity. Because investigation of functional signi®cance requires instruments assessing behavioural regulations, instrument development took place. Results partially supported the validity of behavioural regulations with respect to leisure-time physical activity. Furthermore, subjective norms were found to represent only the controlling dimension of functional signi®cance. Attitudes and perceived behavioural control were found to represent both the controlling and informational dimensions of functional signi®cance. Results are discussed in relation to assumptions underlying the Theories of Reasoned Action and Planned Behaviour and the Theory of Trying. Implications for theory development are made. # 1998 John Wiley & Sons, Ltd. CCC 0046±2772/98/030303±20$17.50 Received 11 August 1996 # 1998 John Wiley & Sons, Ltd. Accepted 30 November 1996 European Journal of Social Psychology Eur. J. Soc. Psychol. 28, 303±322 (1998) *Address for correspondence: Stuart Biddle, Professor of Exercise & Sport Psychology, Department of PE, Sports Science and Recreation Management, Loughborough University, Loughborough, Leics LE11 3TU, UK. Fax: ‡44 1509 223 971. e-mail: [email protected]. Parts of this research are from the MSc in Exercise & Sport Psychology dissertation submitted to the University of Exeter by the ®rst author under the supervision of the second author. Both authors are now at Loughborough University.