partner/best friend thinks about this?’). Again, it is assumed that an individual will only
have a limited number of referents in mind when considering a behaviour. Thus the
more people (whose approval is seen to be important) who are thought to approve of
the action, the more positive the subjective norm. Judgements of PBC are influenced
by control beliefs concerning whether one has access to the necessary resources and
opportunities to perform the behaviour successfully, weighted by the perceived power,
or importance, of each factor to facilitate or inhibit the action. These factors include
both internal control factors (information, personal deficiencies, skills, abilities,
emotions) and external control factors (opportunities, dependence on others, barriers).
As for the other types of beliefs, it is assumed that an individual will only consider a
limited number of control factors when considering a behaviour. So, for example, in
relation to quitting smoking, a strong PBC to quit smoking would be expected when
a smoker believes there are more factors that facilitate than inhibit quitting smoking,
especially if the inhibiting factors do not have strong effects on the feasibility of quitting.
The TPB has at least two advantages over the extended HBM. First (as in PMT),
health beliefs are seen to affect behaviour indirectly, in this case through attitude and
intention. Thus the model outlines a mechanism by which particular beliefs combine
to influence motivation and action. Second, the model takes account of social
influence on action. The TPB has been widely tested and successfully applied to the
understanding of a variety of behaviours (for reviews see Ajzen, 1991; Conner and
Sparks, 2005, 2015). For example, in a meta-analysis of the TPB Armitage and Conner
(2001) reported that across 154 applications, attitude, subjective norms and PBC
accounted for 39 per cent of the variance in intention, while intentions and PBC
accounted for 27 per cent of the variance in behaviour across 63 applications. Inten -
tions were the strongest predictors of behaviour, while attitudes were the strongest
predictors of intentions (see McEachan et al., 2011 for a review of applications of the
TPB to health behaviours).
The TPB has also informed a number of interventions designed to change
behaviour. For example, Hill, Abraham and Wright (2007) employed a randomized
controlled trial to test the effectiveness of a TPB-based leaflet compared to a control
in promoting physical exercise in a sample of school children. The leaflet condition
compared to the control condition significantly increased not only reported exercise
but also intentions, attitudes, subjective norms and PBC. Additional analyses indicated
that the impact on exercise was mediated (i.e. partly explained) by the increases the
leaflet had produced (compared to the control group) in intentions and PBC.
Recent work with the TPB (see Conner and Sparks, 2005, 2015) has suggested the
value of dividing attitude, subjective norm and PBC each into two components to
form the ‘two-factor TPB’ (Figure 7.4). Attitude is divided into an affective or experi -
ential component and a cognitive or instrumental component. The first concerns beliefs
and evaluations about how it will feel to perform the behaviour while the second
includes beliefs and evaluation about other consequences. So, for example, quitting
smoking might be perceived as both unenjoyable (affective evaluation) but beneficial
(cognitive evaluation). As well as subjective norms (defined above) the two-factor
model includes descriptive norms. Descriptive norms refer to perceptions of what
others are doing (‘e.g. all my friends are doing it’) rather than beliefs about others’
approval of the target individual performing the behaviour. For example, a smoker
might believe that important others approved of him or her quitting but those other
150 MOTIVATION AND BEHAVIOUR