Behavioural Change Theories

a) Ajzen's Theory of Planned Behaviour (1991)

The theory of planned behaviour (TPB) is a behavioural science theory.

According to this theory, whether or not a person performs a given behaviour depends upon a combination of particular individual and social factors. The presence or absence of these factors can therefore predict a person's future behaviour.

In designing interventions intended to change people's behaviour, you need to have an understanding of how you expect that behaviour change to occur.

Ajzen's Theory of Planned Behaviour is one of several behavioural theories that could be used to inform the design of interventions, and help to estimate their effects.

A link between attitude and behaviour:

TPB is based on intentions – the more a person intends to do something, and the more motivation they have, the more likely they are to actually do it.

Three key factors are said to determine the strength of someone's intention. These are:

  1. Self-efficacy (perceived ability)
  2. Attitude
  3. Social norms


Self-efficacy is a person's self-rated ability to perform a particular behaviour. Their perceived ability to perform a particular behaviour varies depending on how much they want to do it. For example: a person may really want to get up early, but may not feel very capable of doing so.

Someone's level of perceived ability can vary depending on what resources they have available. For example: a person may feel more capable of getting up early if they know that they have a friend to call them in the morning, or the money to buy a very good alarm clock! TPB states that if a person has low self-efficacy towards a particular behaviour, then they are very unlikely to attempt to perform that behaviour. For example: they may not even bother to try to get up early, as they already feel that they won't be able to.

Conversely, someone who believes that they can perform a particular behaviour successfully, regardless of their actual (objective) ability to do so, is highly likely to attempt it.

Attitude toward the behaviour:

If a person thinks that performing a particular behaviour will result in positive consequences for themselves, then they are more likely to have a positive attitude towards that behaviour.

For example: If someone speeds to get to an appointment, and as a result of that speeding behaviour they make it on time avoiding the negative consequences of being late; then they are likely to think positively about speeding.

Likewise, if an individual believes a particular behaviour will result in negative consequences, then they will view that behaviour unfavourably.

For example: If a person exceeds speed limits, even if they get to the appointment on time, but receive a speeding ticket, they are likely to think negatively about speeding.

Social Norms:

Most behaviour has social norms associated with it. Social norms are felt as pressure to conform, or not conform, to a particular behaviour. This pressure can come from friends, family, work colleagues, neighbours, peers, and any significant 'other' to whom a person refers to in forming their own beliefs and values. For example: If a person's highly respected friends and work colleagues believe that speeding is generally OK, then that person is likely to share the same view.

Social Norms

Applied example of TPB:

A young driver believes that she has the skills and the experience to drive at 50mph in a 30mph zone (high self-efficacy). Her family and friends typically drive at this speed in the same area (approving social norms), and she thinks that she will be able to save time and avoid being late for an appointment, if she continues at this speed (positive attitude). Also, she does not think that she will get caught by the police (high self-efficacy) so is not worried about getting a ticket (positive attitude).

Based on TPB, interventions to change this young driver's behaviour would focus on reducing her perceived ability to drive at 50mph in a 30mph zone: by educating her about stopping distances and local enforcement for instance, and on changing her currently positive attitude towards speeding by making her more aware of the potential negative consequences of doing so. The opinions of her friends and family could also be targeted through local publicity campaigns.


  1. Ajzen, I. (1991) The Theory of Planned Behaviour Organisational Behaviour and Human Decision Processes Vol. 50. pp.179-211
  2. Ajzen's own website

b) Gibbons and Gerrard's Willingness Model (1995)

The theory of planned behaviour explains behaviour as a product of intention. Whilst this is a useful theory, sometimes behaviour occurs without any pre-planned intent. Behaviour for instance can be irrational, or a purely emotional, spur of the moment, reaction. Not all behaviour is planned!

Gibbons and Gerrard realised this and developed their Willingness Model to explain behaviour change specifically in young people. Gibbons and Gerrard believe that young people are less likely to be able to predict how they will behave in certain situations, as they have less life-experience on which to base their judgements. Likewise, young people are more likely to take risks.

Intention is still a key trigger for behaviour change but Gibbons and Gerrard think that behavioural willingness is another key trigger.

Behavioural willingness is how likely a person thinks they are to perform a particular behaviour, depending on the circumstances. This is different to intending to perform, or not to perform, certain behaviour. Willingness acknowledges that behaviour may depend upon the particular situation a person finds themselves in – they may not intend to drive whilst drunk for example, but under pressure from friends and the need to get home, they might do so.

Discussing this difference between intention and willingness may help young people to better understand their own risk taking behaviour.

Social Images

Willingness of a young person to perform a particular behaviour is said to be affected by the social images they associate with that behaviour. Young people are especially conscious of social images, and their behaviour typically occurs in a social space, i.e. with friends. If a particular behaviour is associated with a negative image then young people will want to avoid being seen performing that behaviour. They will want to avoid a negative social reaction.

The implication for road safety is therefore to build negative social reactions to a risky behaviour, thus inhibiting a young person's willingness to perform that behaviour.

Similarly, building positive images of safer behaviour may encourage young people to want to associate themselves with that image.

For young people intent on taking risks however, efforts to make that risky behaviour seem less socially acceptable, and a less desirable image for them to be associated with, may not work.


  1. Gibbons, F. X., & Gerrard, M. (1995). Predicting young adults' health risk behaviour. Journal of Personality and Social Psychology, 69, pp.505-517.
  2. Gibbons, F. X., Gerrard, M. & Lane, D. J. (2003). A social-reaction model of adolescent health risk. In J. M. Suls & K. A. Wallston (Eds.) Social Psychological Foundations of Health and Illness, (pp 107 – 136). Oxford, England: Blackwell.
  3. Gerrard, M., Gibbons, F.X., Brody, G.H., Murry, V.M., Cleveland, M.J.*, & Wills, T.A. (2006). A theory-based dual focus alcohol intervention for pre-adolescents: Social cognitions in The Strong African American Families Program. Psychology of Addictive Behaviours, 20, 185 - 195.