Robert Putnam, an influential social capital researcher, visited BYU nearly two years ago to discuss how social connections are on the decline. Here is good summary of Putnam's talk on BYU NewsNet. His research during the past decade has shown a negative trend in that people are socially connecting less these days. The speech gave fuel to the research on social networks that I had been involved in and has been a strong motivation to our current work on social capital.
Figure 1. "The TV Connection" shows that group membership tends to decline as television viewing increases among those having twelve or more years of education. (see The Strange Disappearance of Civic America)
Empirical studies on group membership, like the study shown in the plot above contribute to the evidence which Putnam uses to support this claim.