There is a brand new Pew Internet Research survey out called The Social Side of the Internet which is all about the impact of the internet on GROUP-FORMING. There's lots of data in here about internet users joining groups, including associations.
The internet is now deeply embedded in group and organizational life in America. A new national survey by the Pew Research Center's Internet & American Life Project has found that 75% of all American adults are active in some kind of voluntary group or organization and internet users are more likely than others to be active: 80% of internet users participate in groups, compared with 56% of non-internet users. And social media users are even more likely to be active: 82% of social network users and 85% of Twitter users are group participants.
I'm only just starting to dig into this but it has so much great stuff that I wanted to share it immediately. See what you think.
It is hard to underestimate the impact of social media and internet use on group engagement. As noted [...], social network site users and Twitter users are much more likely than online group members who do not use these tools to say that the internet has a major impact on almost all aspects of their group engagement. This relationship is confirmed in regression analyses when other important factors such as age, education, income, personal efficacy, religiosity, and trust are controlled.In fact, among all of these key predictors of online behavior and group involvement, being a daily internet user, being a social network site user, and being a Twitter user are among the most powerful predictors of whether people perceive the internet as having a major impact on their ability to find groups that match their interests, bring others into their groups, keep up with the groups they belong to, organize group activities, contribute money or volunteer their time, and even create their own groups. Moreover, among active group participants who are online, social network site use, Twitter use, and daily internet use are more powerful predictors of discovering new groups online, participating in "a lot more groups," and spending more time participating in groups than other factors such as age, income, education, and efficacy.