Critically Evaluate the Extent Critically Evaluate the Extent to which the Theory of to which the Theory of Planned Behaviour can Planned Behaviour can Predict Healthy Eating Predict Healthy Eating

BehavioursBehaviours

IntroductionIntroduction

• This presentation intends to: -This presentation intends to: -

1)1) Explain the model and why it is Explain the model and why it is required.required.

2)2) Apply the model to healthy eating.Apply the model to healthy eating.3)3) Critically evaluate its effectiveness at Critically evaluate its effectiveness at

predicting healthy eating behaviour predicting healthy eating behaviour using recent psychological research.using recent psychological research.

Theory of Planned Theory of Planned Behaviour Ajzen (1988, ‘91)Behaviour Ajzen (1988, ‘91)

• Theory of Planned Behaviour suggests: -Theory of Planned Behaviour suggests: -– ““behaviour is deliberate and therefore can be behaviour 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 Behaviour is not always completely under a

person’s control.person’s control.– Ajzen extended TRA to include ‘Perceived Ajzen extended TRA to include ‘Perceived

Behavioural Control’ (PBC)Behavioural Control’ (PBC)

Theory of Planned Theory of Planned Behaviour Ajzen (1988, ‘91)Behaviour Ajzen (1988, ‘91)

Ajzen, I. (1991). The theory of planned behavior. Ajzen, I. (1991). The theory of planned behavior. Organizational Behavior and Human Decision Processes,Organizational Behavior and Human Decision Processes, 50, 50, p. 179-211. p. 179-211.

Theory of Planned Theory of Planned Behaviour Ajzen (1988, ‘91)Behaviour Ajzen (1988, ‘91)

• Most widely used model in predicting healthy Most 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 (subjective Perceived 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 and Predictions can be made about intentions and actual behaviour.actual behaviour.

• Interventions may be implemented to change Interventions may be implemented to change peoples’ intentions.peoples’ intentions.

• National obesity rates are on the increase in National 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.

Government InterventionsGovernment Interventions• British Heart Foundation:British Heart Foundation:

– Programmes to raise public awareness of potential risksProgrammes to raise public awareness of potential risks– 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 which facilitate/ TPB may help identify barriers which facilitate/ inhibit health eating behaviour.inhibit health eating behaviour.

Armitage and Conner Armitage and Conner (1999).(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; intentions, Questionnaire – Px answered questions relating to; intentions,

attitudes, subjective norms, PBC, self – efficacy and behaviour.attitudes, subjective norms, PBC, self – efficacy and behaviour.• FindingsFindings::

– Support for TPB as they displayed strong correlation between Support for TPB as they displayed strong correlation between intention and behaviour and also between intention and its direct intention and behaviour and also between intention and its direct antecedents.antecedents.

– Suggests TPB is useful in predicting consumption of low fat diets.Suggests TPB is useful in predicting consumption of low fat diets.

Povey, Conner, Sparks, James Povey, Conner, Sparks, James and Shepherd (2000).and 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 control measures.to assess relations between control beliefs and control 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 eating A 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-efficacy being Less good at predicting actual behaviour, with self-efficacy being

more effective than perceived control. more effective than perceived control.

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 eating 139 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 and No support for TPB - no association between intention and

healthy eatinghealthy eating..– Most predictive barriers were availability and taste of food.Most predictive barriers were availability and taste of food.– Boys – subjective norms.Boys – subjective norms.– Girls – barriers.Girls – barriers.

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 and Aware of the risks of excessive fat consumption and

maintain behaviours regardless.maintain behaviours regardless.

– Highlighting these factors may prove futile Highlighting these factors may prove futile when developing interventions.when developing interventions.

EvaluationEvaluation• Povey et al (2000)Povey et al (2000)

– Ambiguous behaviours difficult to predict using TPB due to Ambiguous behaviours difficult to predict using TPB due to interpretations.interpretations.

– Specific much easier to predict as they are open to little Specific 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.

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 al Terry and O’Leary (1995) & Sparks et al (1997)(1997)– Perception of difficulty greater predictor than Perception of difficulty greater predictor than

perceptions of control.perceptions of control.• May be useful to include self efficacy into May be useful to include self efficacy into

TPB alongside PBC.TPB alongside PBC.

EvaluationEvaluation• TPB assumes humans are rational beings TPB assumes humans are rational beings

who always carry out their intentions.who always carry out their intentions.• Misconception that people weigh up their Misconception that people weigh up their

intentions with the other factors stated to intentions with the other factors stated to argue whether or not to engage in healthy argue whether or not to engage in healthy behaviour.behaviour.

• In reality, people tend to be much more In reality, people tend to be much more chaotic.chaotic.– Eat unhealthy food, then retrospectively generate Eat unhealthy food, then retrospectively generate

arguments in order to justify their behaviour.arguments in order to justify their behaviour.

EvaluationEvaluation• Gap between intentions and behaviour.Gap between intentions and behaviour.

– Due to presentation of statements relating to Due 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.

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 – much Povey et al (2000) 287 members of public – much

more generalisedmore generalised• Although arguably specified sample due to the types of Although arguably specified sample due to the types of

people responding to an advert?people responding to an advert?• NB: Questionnaires administered to larger NB: Questionnaires administered to larger

populations.populations.– Small samples may reflect lack of interestSmall samples may reflect lack of interest

ConclusionConclusion• Vast understanding to be gained from Vast understanding to be gained from

using TPB.using TPB.– Requires further manipulation to become Requires further manipulation to become

successful predictor of healthy behaviours.successful predictor of healthy behaviours.• Food frequency questionnaires (Povey et Food frequency questionnaires (Povey et

al, 2000).al, 2000).– Some foods may not easily fit into available Some foods may not easily fit into available

categories.categories.

Conclusion Conclusion • Self – efficacy more effective at predicting Self – efficacy more effective at predicting

ambiguous behaviours.ambiguous behaviours.• PBC more effective at predicting specific PBC more effective at predicting specific

behaviours.behaviours.• TPB may be more effective if both these TPB may be more effective if both these

aspects were included to predict aspects were included to predict behaviours based on people’s perceived behaviours based on people’s perceived control and perception of their ability to control and perception of their ability to carry out the behaviour. carry out the behaviour.

Any Questions???Any Questions???