Jarvela, Sanna
Elsiever, 2011
Buku Teks
International Association of Gerontology; edited by Clark Tibbitts and Wilma Donahue
Columbia University Press, 1962
Buku Teks SO
edited by Albert I. Wertheimer and Mickey C. Smith
University Park Press, 1981
Buku Teks
Larkin, Mary
McGraw-Hill, 2011
Buku Teks
Edey, Harold C.
Hutchinson University Library, 1969
Buku Teks