This thesis examines the main predictors of political involvement from a
social identity perspective, thus the main questions addressed is when people decide
to take collective action in relation to shared ideas. It is argued that group selfdefinition
should predict intentions to undertake political behaviours. Surprisingly the
existing literature does not unequivocally show that the strength of subjective group
membership is a good predictor of group behaviour in general, or political
behavioural intentions in particular. The thesis proposes four key solutions to this
problem. The first is that the relationship will tend to be strong when groups are in
conflict: intergroup conflict seems to help organize behaviour into oppositional forms.
Secondly, the group membership will be a stronger predictor when the groups are
normatively relevant to the predicted behaviour. As social identity theorists have long
argued, group behaviour is only predicted by group membership when that behaviour
is consistent with a relevant norm for the group. Thirdly, the relationship will tend to
be strong when relevant groups are chosen, and the focus here is on opinion-based
groups: groups defined on the basis of a shared opinion. Fourthly, the relationship will
tend to be strong when the degree or strength of self-categorization is measured
appropriately. Here the argument is that measures of certainty of self-definition as a
group member capture these constructs best for opinion-based groups. To sum up,
self-definition as an opinion-based group member should strongly predict political
involvement in conditions of intergroup conflict and when the behaviours involved
are highly consistent with the norms of the specific salient group membership.
In addition to the main prediction that group self-defmition should increase
political group behaviour it was also expected that, in line with self-categorization
theory, measures which better captured salience of opinion-based group membership should be stronger and more direct predictors of behavioural intentions than standard
social identification measures. Consequently self-definition as an opinion-based group
member was assessed using standard identification scales but also some new items
which were aimed to capture salience of opinion-based group membership. In
particular, it was argued that certainty of self-definition as a group member holding a
certain opinion would be the best indicator of salience, but only especially so in
opinion-based groups.
These ideas were explored in a series of six studies (two surveys and four
experiments). The results of the first two experiments using minimal opinion-based
groups show that intergroup conflict had some impact on the main variables involved,
and suggested the direction for the next studies in which the link between opinionbased
group self-definition and political behavioural intentions was directly
investigated. Results from Studies 3, 4, and 5 strongly supported the hypothesis that
the salience measure employed predicted political behavioural intentions over and
above identification. However, Study 5 provided no evidence that conflict enhanced
the expected relationship. Finally, the results of Study 6 suggest that the salience
measure is highly sensitive to the normative context and is a good predictor of
political behavioural intentions but only especially so for the highly normative and
validated behaviours.
The conclusion reached is that certainty of self-definition as an opinion-based
group member is an excellent predictor of normatively relevant political behavioural
intentions. The success of this measure stems for the fact that it captures the selfcategorization
theory construct of salience more accurately than do standard measures
of social identification and this is almost surely because these measures capture the
(relatively) enduring aspects of salience that are associated with perceiver readiness. In summary, self-definition as a group member is indeed a good predictor of validated
normative political behavioural intentions in opinion-based groups, even where there
is not explicit intergroup conflict
