Theory of Planned Behaviour


  • Ajzen (1989) proposed TPB to explain the cognitive factors that led to a person to engage in behaviour. It is a cognitive explanation which states that, according to this definition, an individual’s decision to engage in a particular behaviour can be directly predicted by their intention to engage in that behaviour.
  • Ajzen also realised that not all behaviours are completely under an individuals control and therefore people perception of control is very important, this relates to the locus of control. Therefore, we have to consider the factors that contribute to a person’s intention to change an unhealthy behaviour.
  • Behavioural Attitude: This is a product of personal views, their attitude towards the behaviour. It is formed on the basis of beliefs about the consequence of it and looking at the value of these consequences.Ways it has been used to prevent addictive behaviour: ONDCP launched a 2005 campaign to lower teenage marijuana use. It was successful due to its influence on attitudes, past campaigns focused on the risk of abuse but many teenagers are not risk avoidant. ONDCP’s ‘Above the Influence’ campaign tried to create a different attitude towards the effect of the use. (E.g. inconsistent with being autonomous and achieving aspirations.) Their target on attitude may be the reasons for its success (Slater et al 2011)Subjective Norms: This is a product of social influence, the individual’s subjective awareness of social norms (what significant others feel is the right thing to do as well as perceptions of what others are actually doing).
    Anti-drug campaigns (often), in an effort to change subjective norms, give out actual data of the % of people engaging in those behaviours.
    For example, some adolescents who smoke may be part of a peer group in which most of the members smoke, therefore making smoking the norm for them. However many adolescents don’t smoke, therefore exposure to the statistics should correct subjective norms and form the basis to an effective campaign. (Wilson and Kolander 2003)

    • Perceived Behavioural Controls: is an individual’s perceived ease or difficulty of performing the particular behaviour. More control people believe themselves to have the stronger their intention. The higher perceived control, the harder the individual will try and the longer they will persevere.
      Godin e al (2002) examined the extent to which the TPB could explain smoking intentions and behaviours in adults intending to give up smoking. Questionnaires and trained interviews at home were used to measure. Participants were surverys at th start and six months later. The researchers found that the 3 elements helped to explain intentions, whereas PBC was the strongest predictor of behaviour. They concluded that prevention programmes should help smokers focus on stopping and alter them of the effort required to modify smoking behaviour.
    • AO2
    • Self-efficacy, as proposed by the TPB is a large part of perceived behavioural control. It suggests that the intention to change behaviour will be stronger in people who have an increased sense of control. Self-efficacy is important in many aspects of addiction prevention. For example, Maser et al (2004) investigated the role of cognitive factors including self-efficacy on abstinence. They found that encouraging an addicts belief in their ability to abstain was related to a positive outcome. Therefore, it was concluded that enhancing self-efficacy should form a primary goal of treatment plans.
    • A limitation of TPB however, is that it predicts intention to change rather than actual behavioural change. Armitage and Conner found in a meta-analysis of studies using this model, that it was successful in predicting intention to change rather than actual behavioural change. This suggests that TPB is primarily an account of intention formation (Aizen and Fishbein 2005) An example comes from Armitage and Conner who suggest that a smoker may think that they will stop within 5 years but will have no plan to do so. As a result, Abraham et al (1998) said that we can make a distinction between a motivational phase that results in the formation of a behavioural intention and a post-decisional phase which involves behavioural initiation and maintenance.
    • Another limitation of TPB is that it is reductionist, as it focuses on the influence of emotions but ignores other influential factors. Topa and Moriano (2010) suggest that group variables, such a peer influence on tobacco addiction, could play a mediating role. Another factors not included is motivation. Klag (2006) studied 350 substance abusers in Australia and found that recovery was consistently more successful in individuals who had decided themselves to give up rather than people who were made to. Additionally, self-determination theory, according to Klag is preferable to TPB because it emphasises the importance of self-motivation.