Historical demography is commonly defined as the application of conventional and non-conventional demographic techniques to data sets from the past (Pressat and Wilson 1985; Smith 2003). Its primary aim is to obtain detailed demographic information and measure demographic changes such as changes in population size, age structure, sex ratio, fertility, mortality, and migration for populations in the past. While estimating the total population in a particular historical setting can be regarded as historical demography at its crudest level, the application of demographic methods to historical source materials and the information generated by such application can be far more elaborate.
Historical demography is closely related to, but differs from, demographic or population history. The former concentrates largely on obtaining the detailed and accurate demographic information for historical populations that provides the foundation for the study of demographic or population history. The latter includes historical demography as a field of enquiry, but covers wider research areas. Demographic history investigates not only the process of past population changes, but also the interrelationship between these changes and a wide range of socio-economic, political, cultural and environmental factors. In general, historical demography tends be more involved in tackling the technical problems of measuring past demographic changes and developing effective methods of analysing historical population data, whereas demographic history is more concerned with the reasons, processes and consequences of major demographic events, especially their long-term impact on socio-economic changes and historical development.
Population changes interact closely with, and play a major part in, political, social and economic changes. Through offering detailed and reliable demographic information about past societies, historical demography can greatly improve our knowledge of history and population history in particular. One of such examples is E. A. Wrigley and R. S. Schofield’s monumental work The Population History of England 1541-1871 (1981). This study, based on extensive empirical evidence and demographic estimates, systematically examines population trends in England over a period of more three hundred years and the population theory proposed by Thomas Robert Malthus (1766-1834). The comprehensive analysis presented in this book provides great insights into demographic patterns and their interplay with socio-economic conditions in the time before and during the industrial revolution. The impact of this work has been felt far beyond the disciplinary confines of historical demography or population history.
While a distinction between historical demography and demographic history can be and has been made by some scholars, it is difficult in practice to draw a clear line between the two approaches and their practitioners. Demographic historians often need to have detailed and accurate demographic information as the foundation for their investigation into population history. Equally, historical demographers also want to examine socio-economic reasons for population changes and the impact of such changes on the society. Because of the close connection between the two disciplines, the discussion presented in this chapter will not be confined within the area narrowly defined by historical demography.
Historical demography is a major component of demography that studies population changes, but it is primarily concerned with applying demographic methods to population data from the past. Demographers wishing to test a proposed hypothesis on contemporary population can, at least theoretically, always collect the data they need according to their research design. Historical demographers, however, have to use existing data – they cannot go back in time to collect the required data. The available data may not have been collected for the purpose of demographic research; they may suffer from various types of registration problems or biases that are often related to the rules or procedures applied in creating the data. This makes historical demographic research a more challenging task than the study of contemporary population issues. For this reason, historical demographers often need to develop new techniques or modify conventional demographic methods so that they can be effectively used in analysing surviving historical data – a point that will be further discussed in section four of this chapter.
Historical demography has made a significant contribution to the development of demography. Through enriching the knowledge about demographic behaviour and population changes in the past, historical demography helps us to gain a better understanding of demographic trends in contemporary societies and future. Louis Henry (1911-1991), the founding father of historical demography, once suggested that, to answer the two questions about population changes that intrigued demographers in the mid-twentieth century, “Where are we?” and “Where are we headed?” we should begin by answering a third, “Where were we yesterday and the day before?”. This reference to the past is, he said, essential for it alone can tell us about the day after (Rosental 2003: 98). The importance of historical demography to the development of demography does not stop here, however. After the Second World War, there was a considerable increase in the interest in population issues throughout the world, and demography as an academic discipline entered a period of rapid development. Mortality and fertility, which had decreased notably in the nineteenth century and the first half of the twentieth century, fell to low levels in most developed countries.