having opportunities for expression of views and political discussion, or contact with organizations of a political nature (Carlisle & Patton, 2013; Oser, Hooghe & Marien, 2013). It should be noted that although the entire population benefits from the cost-cutting of political participation in its online modality, it is the people of lower socioeconomic status who experience the most important changes around their ability to develop the above behaviours. On the contrary, the most advantaged social sectors have enjoyed greater opportunities to express themselves, inform themselves and maintain connections with political actors or associations since the pre-internet period (Best & Krueger, 2005; Brady, Verba & Schlozman, 1995).

Added to this is the ability of social network sites to stimulate digital political behaviours in people with lower incomes, lower education and little interested, putting in place mechanisms such as incidental exposure to political information and mobilizing stimuli (Kim, Chen & Gil de Zúñiga, 2013; Gustafsson, 2012; Valenzuela, 2013), availability of permanent audiences for expression of the individual political voice (Gil de Zúñiga et al., 2014) and expansion of social capital in interactive environments (Gil de Zúñiga et al., 2012; Valenzuela, Park & Kee, 2009). The above coincides in part with the research conducted by Valeriani and Vaccari (2016) from representative samples from different European countries, where incidental exposure to political information via social media was found to be more intensely related with online political participation when it comes to people who reported less interest in politics. This reasoning suggests that the informational and expressive uses of platforms such as Facebook or Twitter may produce differential gains in cognitive and attitudinal terms, benefiting people with lower socioeconomic status to a greater extent. Thus, these differential gains increase more strongly the willingness to participate politically in the less favoured social groups. If such a democratizing effect occurs, political use of social media would be expected to stimulate offline political participation more intensely in those citizens with less socioeconomic status. This would also apply to political protest behaviours.

On the other hand, political groups are suitable spaces for the cultivation of interpersonal ties and contact with other organizations that share common interests (Schussman & Soule, 2005). With their arrival, the internet and social network sites have not only drastically reduced the communication costs of political organizations and social movements, they have also brought a more decentralized character to their operation, creating opportunities for its members to take a more active and autonomous role in promoting organizational objectives (Gibson, 2015; Theocharis et al., 2015). Such conditions could intensify the cognitive and attitudinal positive effects generated by political use of platforms such as Facebook or Twitter.

First, the consumption of political information via social network sites acquires higher mobilizing quality for those belonging to offline political groups. This is because political groups operate as mobilization networks through which information directly linked to the development of political initiatives and activities in the real world circulates, such as invitations, calls, proposals for action, meeting places, activist agendas, among others (Best & Krueger, 2005; Carty, 2010; Lemert, 1981; Micó & Casero-Ripollés, 2014). Given these conditions, the informational use of social network sites by those belonging to political groups has a greater mobilizing information burden.

Second, offline political groups have a number of characteristics that favour the cognitive and attitudinal processes associated with both political expression and discussion. Although the relationship between membership of civil society