organizations and social capital has been studied for a long time (Putnam 2000), Conroy et al. (2012) emphasize that political groups promote political participation through two mechanisms: (a) the creation of stimulating conditions for political discussion and (b) mutual control of members’ activities and contributions. However, the interaction that takes place on social media sites only reproduces the first mechanism properly, while the possibilities of control suffer limitations due to the lack of face-to-face contact. In this sense, the digital expression of opinions is more likely to be feedback thanks to the contributions of the other members of the organization, who share an interest in politics as opposed to the rest of the contacts list.

This raises the propensity to participate in electronic discussions on political issues for those who belong to offline political groups, even more so if these groups are present on social media. Membership of offline political groups therefore ensures to a greater extent that the informational and expressive uses of social network sites generate favourable returns in terms of political learning, civic engagement and group identity. Aspects of vital importance for the gestation of collective actions, particularly necessary for political protest (Schussman & Soule, 2005; Valenzuela et al., 2012).

Additionally, although users are more inclined to include similarly thinking people in their contact list, which has been defined as social selectivity (Campbell & Kwak, 2011), offline political groups limit to some extent this possibility. Although in general, those who make up a political organization or social movement share common interests, this does not imply that there can be heterogeneous points of view and opinions when more specific issues are addressed. In this regard, studies have shown that the deliberative quality of political discussion increases when there is heterogeneity of views, which in turn improves the gains of political knowledge (Mutz, 2002). Finally, political messages generated by members of organizations through social network sites are likely to have a greater mobilizing burden. As mentioned, social media allows members of political groups to become more actively and autonomously involved in boosting organizational agendas. Thus, members have greater incentives to generate mobilizing stimuli from the political use of their Facebook or Twitter accounts. Mobilizing actions may be directed to other members as messages that propose, convene or promote action, or to non-militant users for recruitment purposes (Gibson, 2015; Gustafsson, 2012). According to the findings of Rojas and Puig-i-April (2009), people who develop mobilization efforts towards others are more likely to engage in offline political participation activities. In short, the sum of the processes described suggests a strengthening of the connection between political behaviour via social media and participation in protest activities for those linked to political groups.

The presented discussion, based on the integration of theoretical and empirical contributions from specialized literature, allows to substantiate the following research hypotheses:

Hypothesis 1 (H1): Political use of social media is positively related to political protest behaviour.

Hypothesis 2 (H2): The relationship between political use of social media and political protest behaviour is moderated by socioeconomic status.

Hypothesis 3 (H3): The relationship between political use of social media and political protest behaviour is moderated by political group membership.