1. Critically Evaluate the ExtentCritically Evaluate the Extent
to which the Theory of Plannedto which the Theory of Planned
Behaviour can Predict HealthyBehaviour can Predict Healthy
Eating BehavioursEating Behaviours
2. IntroductionIntroduction
• This presentation intends to: -This presentation intends to: -
1)1) Explain the model and why it is required.Explain the model and why it is required.
2)2) Apply the model to healthy eating.Apply the model to healthy eating.
3)3) Critically evaluate its effectiveness atCritically evaluate its effectiveness at
predicting healthy eating behaviourpredicting healthy eating behaviour
using recent psychological research.using recent psychological research.
3. Theory of Planned BehaviourTheory of Planned Behaviour
Ajzen (1988, ‘91)Ajzen (1988, ‘91)
• Theory of Planned Behaviour suggests: -Theory of Planned Behaviour suggests: -
– ““behaviour is deliberate and therefore can bebehaviour is deliberate and therefore can be
planned and predictedplanned and predicted ““
• Extention of Ajzen and Fishbein (1975, ‘80)Extention of Ajzen and Fishbein (1975, ‘80)
Theory of Reasoned Action (TRA).Theory of Reasoned Action (TRA).
– Behaviour is not always completely under a person’sBehaviour is not always completely under a person’s
control.control.
– Ajzen extended TRA to include ‘PerceivedAjzen extended TRA to include ‘Perceived
Behavioural Control’ (PBC)Behavioural Control’ (PBC)
4. Theory of Planned BehaviourTheory of Planned Behaviour
Ajzen (1988, ‘91)Ajzen (1988, ‘91)
Ajzen, I. (1991). The theory of planned behavior.Ajzen, I. (1991). The theory of planned behavior. OrganizationalOrganizational
Behavior and Human Decision Processes,Behavior and Human Decision Processes, 50, p. 179-211.50, p. 179-211.
5. Theory of Planned BehaviourTheory of Planned Behaviour
Ajzen (1988, ‘91)Ajzen (1988, ‘91)
• Most widely used model in predicting healthyMost widely used model in predicting healthy
eating behaviour.eating behaviour.
• Assumes people eat healthy foods based on:Assumes people eat healthy foods based on:
– Positive attitudes towards them (attitudes).Positive attitudes towards them (attitudes).
– Perceived social pressure to continue (subjectivePerceived social pressure to continue (subjective
norms).norms).
– Belief that they can maintain healthy eating (PBC).Belief that they can maintain healthy eating (PBC).
• Predictions can be made about intentions andPredictions can be made about intentions and
actual behaviour.actual behaviour.
• Interventions may be implemented to changeInterventions may be implemented to change
peoples’ intentions.peoples’ intentions.
6. • National obesity rates are on the increase inNational obesity rates are on the increase in
western countries.western countries.
– 46% of men and 32% of women are overweight.46% of men and 32% of women are overweight.
– 17% of men and 21% of women are obese.17% of men and 21% of women are obese.
• Overweight and obesity increase with age.Overweight and obesity increase with age.
– 28% of men and 27% of women aged 16-24.28% of men and 27% of women aged 16-24.
– 76% of men and 68% of women aged 55-64.76% of men and 68% of women aged 55-64.
• Obesity rates have doubled since the mid-Obesity rates have doubled since the mid-
1980's.1980's.
(Collins, 2007)(Collins, 2007)
UK Obesity Statistics.UK Obesity Statistics.
7. Government InterventionsGovernment Interventions
• British Heart Foundation:British Heart Foundation:
– Programmes to raise public awareness of potentialProgrammes to raise public awareness of potential
risksrisks
– Eg. Coronary Heart Disease.Eg. Coronary Heart Disease.
– National campaigns:National campaigns:
– Five portions of fruit and veg.Five portions of fruit and veg.
– Decreasing salt intake.Decreasing salt intake.
– Lower cholesterol.Lower cholesterol.
– Decreasing saturated fat intake.Decreasing saturated fat intake.
– Two portions oily fish.Two portions oily fish.
• TPB may help identify barriers whichTPB may help identify barriers which
facilitate/ inhibit health eating behaviour.facilitate/ inhibit health eating behaviour.
8. Armitage and Conner (1999).Armitage and Conner (1999).
• Aims:Aims:
1.1. to apply TPB to eating a low-fat diet.to apply TPB to eating a low-fat diet.
2.2. to consider differences between self-efficacy and PBC.to consider differences between self-efficacy and PBC.
3.3. to examine self identity as an addition to the model.to examine self identity as an addition to the model.
4.4. to identify beliefs to provide targets for interventions.to identify beliefs to provide targets for interventions.
• Method:Method:
– Collected data from 221 students.Collected data from 221 students.
– Questionnaire – Px answered questions relating to;Questionnaire – Px answered questions relating to;
intentions, attitudes, subjective norms, PBC, self – efficacyintentions, attitudes, subjective norms, PBC, self – efficacy
and behaviour.and behaviour.
• FindingsFindings::
– Support for TPB as they displayed strong correlationSupport for TPB as they displayed strong correlation
between intention and behaviour and also between intentionbetween intention and behaviour and also between intention
and its direct antecedents.and its direct antecedents.
– Suggests TPB is useful in predicting consumption of low fatSuggests TPB is useful in predicting consumption of low fat
diets.diets.
9. Povey, Conner, Sparks, James andPovey, Conner, Sparks, James and
Shepherd (2000).Shepherd (2000).
• Aims:Aims:
1.1. to examine the distinction between self-efficacy and PBC.to examine the distinction between self-efficacy and PBC.
2.2. to assess relations between control beliefs and controlto assess relations between control beliefs and control
measures.measures.
• Method:Method:
– 287 members of general public.287 members of general public.
– Questionnaire – attitudes towards food.Questionnaire – attitudes towards food.
– Answered questions relating to; intentions, attitudes. PBC,Answered questions relating to; intentions, attitudes. PBC,
subjective norms, controls beliefs and perceived need.subjective norms, controls beliefs and perceived need.
– A month later – follow up questionnaire about actual eatingA month later – follow up questionnaire about actual eating
behaviour.behaviour.
• Findings:Findings:
– Showed support for TPB as components predict intentions.Showed support for TPB as components predict intentions.
– Less good at predicting actual behaviour, with self-Less good at predicting actual behaviour, with self-
efficacy being more effective than perceived control.efficacy being more effective than perceived control.
10. Fila and Smith (2006).Fila and Smith (2006).
• Aims:Aims:
1.1. to investigate efficacy of TPB to predict healthy eating.to investigate efficacy of TPB to predict healthy eating.
• Method:Method:
– 139 Native American youths given a survey to assess eating139 Native American youths given a survey to assess eating
behaviour using the TPB constructs.behaviour using the TPB constructs.
– Added 2 extra constructs; barriers and self-efficacy.Added 2 extra constructs; barriers and self-efficacy.
– Body Mass Index (BMI) was also calculated.Body Mass Index (BMI) was also calculated.
• FindingsFindings::
– No support for TPB - no association between intention andNo support for TPB - no association between intention and
healthy eatinghealthy eating..
– Most predictive barriers were availability and taste ofMost predictive barriers were availability and taste of
food.food.
– Boys – subjective norms.Boys – subjective norms.
– Girls – barriers.Girls – barriers.
11. EvaluationEvaluation
• Armitage and Conner (1999)Armitage and Conner (1999)
– Intentions best predictors of eating low fat diet.Intentions best predictors of eating low fat diet.
• Behaviour volitional and not affected by PBC.Behaviour volitional and not affected by PBC.
• Largely dependent on self efficacy and attitudes.Largely dependent on self efficacy and attitudes.
– Risk of CHD not facilitating factor.Risk of CHD not facilitating factor.
• Aware of the risks of excessive fat consumption andAware of the risks of excessive fat consumption and
maintain behaviours regardless.maintain behaviours regardless.
– Highlighting these factors may prove futile whenHighlighting these factors may prove futile when
developing interventions.developing interventions.
12. EvaluationEvaluation
• Povey et al (2000)Povey et al (2000)
– Ambiguous behaviours difficult to predict using TPB due toAmbiguous behaviours difficult to predict using TPB due to
interpretations.interpretations.
– Specific much easier to predict as they are open to littleSpecific much easier to predict as they are open to little
interpretation.interpretation.
• Clear targetsClear targets
• Easier to derive intentionsEasier to derive intentions
• Williams (1995)Williams (1995)
– May help improve nutrition guidelines.May help improve nutrition guidelines.
– Individuals can monitor and control their eating behaviour.Individuals can monitor and control their eating behaviour.
13. EvaluationEvaluation
• Armitage and Conner (1999)Armitage and Conner (1999)
– Px struggled to separate the two concepts.Px struggled to separate the two concepts.
• Self efficacy – perception of own ability.Self efficacy – perception of own ability.
• PBC – external inhibiting factors.PBC – external inhibiting factors.
• Povey et al (2000)Povey et al (2000)
– Self efficacy much better predictor.Self efficacy much better predictor.
• Terry and O’Leary (1995) & Sparks et alTerry and O’Leary (1995) & Sparks et al
(1997)(1997)
– Perception of difficulty greater predictor thanPerception of difficulty greater predictor than
perceptions of control.perceptions of control.
• May be useful to include self efficacy intoMay be useful to include self efficacy into
TPB alongside PBC.TPB alongside PBC.
14. EvaluationEvaluation
• TPB assumes humans are rational beings whoTPB assumes humans are rational beings who
always carry out their intentions.always carry out their intentions.
• Misconception that people weigh up theirMisconception that people weigh up their
intentions with the other factors stated tointentions with the other factors stated to
argue whether or not to engage in healthyargue whether or not to engage in healthy
behaviour.behaviour.
• In reality, people tend to be much moreIn reality, people tend to be much more
chaotic.chaotic.
– Eat unhealthy food, then retrospectively generateEat unhealthy food, then retrospectively generate
arguments in order to justify their behaviour.arguments in order to justify their behaviour.
15. EvaluationEvaluation
• Gap between intentions and behaviour.Gap between intentions and behaviour.
– Due to presentation of statements relating toDue to presentation of statements relating to
behavioural intentions.behavioural intentions.
• Don’t address immediate or long term intentions.Don’t address immediate or long term intentions.
• Much more vague – eat healthy at some point.Much more vague – eat healthy at some point.
• Povey et al (2000) and Fila and Smith (2006):Povey et al (2000) and Fila and Smith (2006):
– TPB – weak predictor of actual behaviour.TPB – weak predictor of actual behaviour.
– No relationship between intention and behaviour.No relationship between intention and behaviour.
• Lifestyle constraints may inhibit behavioural change.Lifestyle constraints may inhibit behavioural change.
16.
17. EvaluationEvaluation
• Major methodological flaw with TPB studies:Major methodological flaw with TPB studies:
– Small/ Specific Sample Sizes:Small/ Specific Sample Sizes:
• Armitage and Conner (1999) – 221 studentsArmitage and Conner (1999) – 221 students
• Fila and Smith (2006) – 139 Native AmericansFila and Smith (2006) – 139 Native Americans
• However:However:
– Povey et al (2000) 287 members of public – muchPovey et al (2000) 287 members of public – much
more generalisedmore generalised
• Although arguably specified sample due to the types ofAlthough arguably specified sample due to the types of
people responding to an advert?people responding to an advert?
• NB: Questionnaires administered to largerNB: Questionnaires administered to larger
populations.populations.
– Small samples may reflect lack of interestSmall samples may reflect lack of interest
18. ConclusionConclusion
• Vast understanding to be gained from usingVast understanding to be gained from using
TPB.TPB.
– Requires further manipulation to becomeRequires further manipulation to become
successful predictor of healthy behaviours.successful predictor of healthy behaviours.
• Food frequency questionnaires (Povey et al,Food frequency questionnaires (Povey et al,
2000).2000).
– Some foods may not easily fit into availableSome foods may not easily fit into available
categories.categories.
19. ConclusionConclusion
• Self – efficacy more effective at predictingSelf – efficacy more effective at predicting
ambiguous behaviours.ambiguous behaviours.
• PBC more effective at predicting specificPBC more effective at predicting specific
behaviours.behaviours.
• TPB may be more effective if both theseTPB may be more effective if both these
aspects were included to predict behavioursaspects were included to predict behaviours
based on people’s perceived control andbased on people’s perceived control and
perception of their ability to carry out theperception of their ability to carry out the
behaviour.behaviour.
