BACKGROUND OF MODELLING IN POPULATION STUDIES

As discussed in Module 1, population research deals with quantitative and qualitative studies of five demographic processes: fertility, mortality, migration, mobility and marriage. It uses both primary and secondary data. The data collected by the researcher is called primary data and the data that already exists in the form of census reports, publications of national sample survey (NSS), administrative statistics collected by different government departments, hospital records, etc. is called secondary data. For those who use quantitative methodology (also considered to be scientific methodology by them) the methods of data collection include sample survey and experiments. For those who use qualitative methodology the methods include fieldwork, observation, ethnographic methods, unstructured and in-depth interviews, and participatory rapid appraisal methods. Quantitative methods are more suited to hypothesis testing while the qualitative methods generate hypothesis and provide subjective meanings.

Among those who prefer quantitative methodology, mathematical models are used quite frequently for estimation, policy experimentation and theory building. They are also used for description of demographic phenomena, interpretation of data, and often to smooth questionable data (Halli and Rao, 1992). They provide answers to many questions which cannot be answered otherwise due to lack of data or observations. For example, they can answer:

• How many people have ever lived on earth?

• In a country having a life expectancy of 70 years, what proportion of people are likely to survive till the age of 65?

• If the present schedule of fertility (i.e., the set of age-specific-fertility rates) remains unchanged, how many children will a woman produce in her life time?