Chambré, S. M.(1993). Voluntarism by elders: Past trends, future prospects. The Gerontologist, 33(2),221–228.
2.
Layton D. N. (1987). Philanthropy and volunteerism: An annotated bibliography. New York: The Foundation Center.
3.
Powell W. W. (1987). The nonprofit sector: A research handbook. New Haven: Yale University Press.
4.
Smith D. H. (1983). Synanthrometrics: On progress in the development of a general theory of voluntary action and citizen participation. In D. H. Smith & J. Van Til (Eds.), International perspectives on voluntary research. Washington, DC: University Press of America.
