Baltes, Paul B. Center for Lifespan Psychology, Max Planck Institute for Human Development, Max Planck Society; Max Planck Institute for Human Development, Max Planck Society;
Smelser, N. J., & Baltes, P. B. (2001). Preface. In International Encyclopedia of the Social and Behavioral Sciences (pp. XXVII-XXIX). Amsterdam: Elsevier Science.