Parajumpers Parka Kodiak,Cheap Parajumpers JacketDemographers have for a long time adopted an empirical approach to the study of the levels and trends of mortality, fertility, and population size. They depend for their analyses on data, usually collected until recent times by government and often for other purposes. Modern demography had its origins in Britain in the second half of the seventeenth century. The major focus of demographers has usually been on mortality, although Cheap Parajumpers Jacket fertility studies predominated in the 1960s and 1970s. Mortality decline in the West only became certain in the late nineteenth century. Until the 1960s the fastest mortality declines were for the young, but an unheralded mortality decline among the old thereafter became important. The world, especially in economically advanced countries, is faced with an increasingly high proportion of old people, explained largely, not by mortality decline, but by fertility decline. Explanations for the mortality transition place different emphases on the role of modern medicine, better nutrition, and behavioral and social change, particularly rising levels of education. Even among the old, at least until 85 years of age, there are wide differentials in mortality by educational level. Analysts have divided the mortality transition into stages: (1) high, pretransitional mortality, (2) early transitional mortality with the decline explained by the conquest of infectious disease, and (3) Parajumpers Parka Kodiak late transitional mortality largely attributable to degenerative disease. Some have now added stage (4), the reduction or delay in death from degenerative causes. Attempts have been made to effect the convergence of demographic and epidemiological approaches to the analysis of mortality, and they have been more successful in the case of medical demographic than in social demographic approaches.