The evidence for your investigation consists of three datasets that are available for statistical analysis using special Web-based software called Survey Documentation and Analysis (SDA) developed by the Computer-assisted Survey Methods Program at the University of California, Berkeley.
One of the major sources of evidence used in Bowling Alone is the General Social Survey (GSS), conducted about every other year since 1972 by the National Opinion Research Center at the University of Chicago. In Appendix I of his book, page 419, Putnam writes,
The two most widely used academic survey archives for American social and political behavior are the National Election Studies (NES) and the General Social Survey (GSS) . . . . and I have relied on both archives in this book. For our purposes, the utility of the NES is limited, however, for it focuses on elections and gives little attention to everyday civic participation. The GSS covers a wider range of activities, although in the domains most central to our interests its continuous coverage is largely confined to formal group membership, church attendance, and social trust.
Read Appendix I, pages 415-420, for some background about the advantages and limitations of using survey data as evidence. For more information about the GSS, go to http://www.norc.org/Research/Projects/Pages/general-social-survey.aspx.
Next, in Appendix I, page 420 of Bowling Alone, Putnam writes,
In the midst of this research, my colleagues and I stumbled onto a second source of annual survey evidence on civic and social activities covering the last quarter of the twentieth century: DDB Needham Life Style Surveys (DDB). Begun in 1975 and still continuing, these extraordinary surveys provide regular barometric readings on scores of social, economic, political, and personal themes, from international affairs and religious beliefs to financial worries and condom usage. With an annual sample of 3,500-4,000, this archive through 1999 contained more than 87,000 respondents over the last quarter of the twentieth century. To the extent that it can be shown to be methodologically reliable, the DDB Needham Life Style archive constitutes one of the richest known sources of data on social change in America in the last quarter of the twentieth century.
For more information on the DDB data, continue reading in Bowling Alone on pages 420-424.
The GSS and the DDB data are survey data at the individual unit of analysis . In other words, social capital, in part, is an attribute that an investigator observes at the individual level simply because it is individuals who have social networks. However, it is also useful at times to combine individual attributes together into data at different levels such as cities, neighborhoods, states, and countries. The term "aggregate data" refers to individual-level data that is combined into data at any of these different levels. In Bowling Alone, Putnam uses aggregate data, along with data about the number of nonprofits in each of the 50 states, in order to build a state-level social capital "index." (You will learn more about indexes in Exercise 4 on this website.) On pages 290-91, Putnam writes,
From a variety of sources, we have combined state-level measures of participation in a range of civic and political activities during the preceding year, including group membership, attendance at public meetings on town or school affairs, service as an officer or committee member for some local organization, attendance at club meetings, volunteer work and community projects, home entertaining and socializing with friends, social trust, electoral turnout, and the incidence of nonprofit organizations and associations . . . . [T]hese fourteen indicators measure related but distinct facets of community-based social capital, and we have combined them into a singe Social Capital Index.