Buhler's basic life tendencies that work toward the fulfillment of life (Buhler, 1935; Buhler & Massarik, 1968)
Buhler, C. (1935). The curve of life as studied in biographies. Journal of Applied Psychology, 19,405-409.
Buhler, C, & Massarik, F. (Eds.). (1968). The course of human life. New York: Springer
Neugarten's (1968,1973) descriptions of personality change in adulthood and old age.
Neugarten, B. L. (1968). The awareness of middle age. In B. L. Neugarten (Ed.), Middle age and aging (pp. 93-98). Chicago: University of Chicago Press.
Neugarten, B. L. (1973). Personality change in late life: A developmental perspective. In C. Eisdorfer & M. P. Lawton (Eds.), The psychology of adult development and aging (pp. 311-335). Washington, DC: American Psychological Association.
Neugarten, B. L., Havighurst, R., & Tobin, S. (1961). The measurement of life satisfaction. Journal of Gerontology, 16, 134-143.