9Birren, James E. and Bengtson, Vern L. Emergent Theories of Aging. Springer Publishing Company, New York, 1988.
10Bengtson, Vern L. Burgess, E. O. and Parrott, T. M. Theory, Explanation, and a Third Generation of Theoretical Development in Social Gerontology. Journal of Gerontology. B.52(2): S72 - S88,1997.