The epidemiological transition theory proposed by Omran in 1971 characterizes the historical development of mortality over time in phases of "the age of pestilence and famine the age of receding pandemics and the age of degenerative and man-made diseases." Demographic transition characterized by a decline first in death rates and then in birth rates occurred over 100 years in the "Western" model but happened much more quickly in countries such as Japan (the "accelerated" model). The "delayed" or "contemporary" model is seen in third world countries where the transition is not complete. The concept of the "Western" model is ill defined and cannot be used without ambiguity because the beginning and end of the epidemiologic transition has not been located in time or clearly defined by Omran. The question remains whether the beginning and end of the epidemiologic transition should be based on trends in all cause mortality or on changes in cause of death patterns. In order for the epidemiologic transition theory to live up to its potential as a powerful framework for the study of disease and mortality in populations especially for the study of historical and international variations and to speculate on the likely consequences of future changes in mortality it is essential to investigate the historical changes in mortality much more thoroughly than has hitherto been done. (EXCERPT)