Theory of Planned Behaviour (AQA A-Level Psychology): Revision Notes
Theory of Planned Behaviour
Introduction
The Theory of Planned Behaviour (TPB) was developed by Icek Ajzen in 1985 and 1991 to explain how people change behaviours over which they can exercise self-control - essentially deliberate behaviours. When applied to addiction, this theory attempts to understand the gap between good intentions (like New Year's resolutions to quit) and actual behavioural change.
Theory of planned behaviour (TPB) - Changes in behaviour can be predicted from our intention to change, which in turn is the outcome of personal attitudes towards the behaviour in question, our beliefs about what others think, and our perceived ability to control our behaviour.
The theory suggests that our intention to perform a behaviour (such as giving up drugs or gambling) can predict whether we will actually change. However, intentions themselves arise from three key psychological influences that work together to shape our motivation to change.
Core Components of the Theory
Personal attitudes
Personal attitudes represent the complete collection of an individual's positive and negative evaluations towards their addictive behaviour. The theory suggests that people weigh up both favourable and unfavourable attitudes to form an overall opinion.
Example: Gambling Addiction Attitudes
Someone with a gambling addiction might list positive aspects such as:
- "It gives me a thrill"
- "I occasionally win"
- "It's an escape from my problems"
However, they might also acknowledge negative consequences like:
- "I lose more money than I win"
- "It makes me tense and anxious"
- "It takes up all my time"
Their overall attitude emerges from balancing these competing evaluations.
The stronger the negative attitudes outweigh the positive ones, the more likely the person is to form an intention to change their behaviour.
Subjective norms
Subjective norms refer to an individual's beliefs about whether the people who matter most to them would approve or disapprove of their addictive behaviour. Importantly, this is about the person's perception of what others think, not necessarily the actual opinions of those people.
When forming subjective norms, individuals consider both what their close friends and family members do themselves and what attitudes they express. For instance, a person with a gambling problem might think: "Most people who matter to me would be very unhappy with me gambling like this," which would make them less likely to intend to continue gambling.
The theory emphasises a crucial distinction: it is not general social approval that matters, but specifically how the person believes their closest relationships would view their particular addictive behaviour.
Perceived behavioural control
This component concerns how much control people believe they have over their behaviour, which relates closely to the concept of self-efficacy. It involves asking whether giving up the addictive behaviour would be easy or difficult for the individual.
Perceived behavioural control depends on both external resources (money, time, support) and internal factors (ability, skill, determination). According to the TPB, this perception can influence behaviour in two ways:
- It directly affects intentions - the more control someone believes they have over stopping gambling, the stronger their intention to do so
- It can also influence behaviour directly, bypassing intention - greater perceived control can lead to harder and more persistent efforts to change
The theory suggests that personal attitudes, beliefs about social approval, and perceived control combine to influence intention to change, which in turn affects the actual effort put into stopping the addictive behaviour.
Research Evidence
Supporting research
Hagger et al. (2011) tested the TPB's predictions about alcohol-related behaviours and found strong support for the theory. Their research demonstrated that all three factors (personal attitudes, subjective norms, and perceived behavioural control) successfully predicted intentions to limit drinking to government guidelines. Importantly, these intentions also predicted the actual number of units consumed after both one month and three months.
The study also found that perceived behavioural control predicted actual alcohol consumption directly, not just through intention, exactly as the theory predicts. This suggests the theory has good predictive validity for some addiction-related behaviours.
Research limitations
However, the research support is not entirely consistent. The time period between forming intentions and measuring behaviour appears crucial - McEachan et al. (2011) conducted a meta-analysis of 237 studies and found that the correlation between intentions and behaviour varied according to the length of time between them.
Intentions may predict behaviour well when measured within about five weeks, but the theory becomes much weaker at predicting long-term behavioural changes. This suggests the TPB may be better at explaining short-term motivation rather than sustained behaviour change.
Major Limitations
The intention-behaviour gap
A major weakness of the TPB is that it cannot adequately explain why actual behaviour often differs from intentions. Rohan Miller and Gwyneth Howell (2005) found strong support for the TPB in predicting gambling intentions among underage teenagers, but the model failed to predict actual gambling behaviour.
This finding raises questions about whether the TPB truly explains behavioural change or simply describes the formation of good intentions that may never be acted upon.
Methodological concerns
The TPB relies heavily on self-report methods to measure attitudes, norms, perceived control, and intentions. This creates several problems:
Key Methodological Issues:
- Social desirability bias may lead participants to exaggerate their intentions to change addictive behaviours to appear more socially acceptable
- Correlational studies cannot establish that drug-related intentions actually cause drug-related behaviours
- The subjective nature of these measures makes it difficult to verify their accuracy
These methodological limitations have led some researchers to conclude that more correlational studies of the TPB are not needed, as they cannot establish causal relationships.
Overemphasis on rational decision-making
The TPB assumes that people make rational, planned decisions about their addictive behaviours. However, this may not reflect the reality of addiction. People often begin using drugs for social and psychological reasons, such as coping with stress, particularly during crisis periods when rational decision-making is unlikely.
The theory struggles to account for emotional factors, cognitive biases, and past experiences that influence both intentions and behaviours. This limitation means the TPB cannot fully explain addictive behaviour and may not be entirely valid as a comprehensive model.
Key Points to Remember:
- The TPB proposes that intention to change addictive behaviour arises from three factors: personal attitudes, subjective norms, and perceived behavioural control
- Personal attitudes involve weighing up positive and negative evaluations of the addictive behaviour
- Subjective norms are beliefs about what important others think of the behaviour, not general social opinion
- Perceived behavioural control relates to self-efficacy and beliefs about available resources for change
- Research shows mixed support - the theory predicts intentions well but struggles with the intention-behaviour gap and long-term behaviour change