The decline in mortality from the mid-18th century in England and other European countries and the more rapid growth in population that occurred up to the mid-20th century have been the subject of investigation and debate among historians, geographers, economists, demographers, and medical specialists. Attention has focused on the relative importance of different factors, such as treatment, care of the sick, measures to control and prevent infectious diseases, living conditions, “standard of living,” nutrition, and changes in the nature of some diseases. Historians and economists have considered the decline in mortality in the context of agricultural and industrial revolutions leading to improvements in food supplies and expansion of economic activity. Studies of the relationship between food supply and death rates in the period leading up to the mortality transition have indicated that many epidemic diseases caused spikes in mortality that were independent of the effects of famine and poor harvests. In earlier premodern times, changes in the infectious disease environment were linked with great transformations in the way of life of humans, particularly the development of agriculture and adaptation to living in settled communities. Eventually urbanization and large-scale migrations led to new ways of living in very different environments, while trade and changes in population size and density brought exposure to new pathogens, different infectious diseases, and changes in the immunological status of individuals and populations.

Industrial development and economic growth in Western countries eventually brought many improvements in living conditions, but the concept of “standard of living” is too general to provide a satisfactory explanation for the decline in mortality and increased life expectancy. It reflects the values of particular sections of society, cultures, and historical periods and masks factors specific to the decline in mortality from particular diseases. It is clearly important to distinguish the specific changes in people's lives that contributed to improved survival chances. In the limited sense of people's own economic circumstances and access to food, shelter, and other basic needs, the concept of “standard of living” can generate hypotheses that are testable with reference to specific indicators.