When the study of population was emerging as a discipline, Warren S. Thompson in his book entitled Population Problems described population studies as being concerned with the following questions related to three broad areas of study:
1. What are the changes that are taking place in the size of the population, and how are these changes brought about? What is the significance of these changes from the standpoint of human welfare?
2. Where are people found and what are the changes taking place in their distribution in communities and in areas?
3. What kind of people are found in any given population group and how do those in one group differ from those in the other?
These questions clearly indicate that the study of population is concerned with its size or numbers, its structure and characteristics, its distribution and the changes taking place in it over a period of time.
It is also implied in this description that the subject matter of population studies includes the study of fertility, mortality, migration and social mobility, that is, the components of change in the size, structure, characteristics and distribution of population.
Before delving any further into the details of the nature of population studies, it is important at this juncture to have a broad understanding of the various concepts used in the description of the scope of population studies.
One important area of study covers the components of population change or the factors responsible for change in the size of population. It must be understood that the population of any place at a specific time is a function of three types of events: births, deaths and migration.
There are four ways in which the number of people in any area can undergo change: (1) children may be born in that area; (2) the inhabitants of that area may die; (3) people from other areas may move into that area; and (4) inhabitants of that area may move out.
These components of population change, namely, births, deaths and migration are identified as fertility, mortality and migration respectively, and are known as demographic or population variables because the size, growth, structure and distribution of any population are determined by them. A study of any population is made through a study of these demographic variables.
It is important to understand at this stage the meaning of population structure and population characteristics.
Population structure implies the age and sex structure of the population and population characteristics include such characteristics as marital status, literacy and educational status, labour force status, etc.
Population characteristics, however, can and do change through "social mobility," that is, through movements of individuals from one status to another for example from "single" to "married" status and also through fertility, mortality and migration.
The scope of population studies is quite wide. On the one hand, this subject is concerned with a quantitative study of the size, structure characteristics and territorial distribution of human populations and the changes occurring in them.
On the other hand, it is concerned with the study of the underlying causes of population phenomena. Thus, a student of population is engaged in describing and comparing the size, structure, characteristics and territorial distribution of the population, and the changes occurring in it through the study of fertility, mortality, migration and social mobility.
He also attempts to explain population phenomena and situations and the changes in them in the context of the biological, social, economic and other setting. For instance, population phenomena take place in a social setting and cannot be studied in isolation.
Hence, while describing, comparing or explaining the determinants and consequences of population phenomena, social phenomena have to be taken into consideration.
It can be seen that the study of population is multidisciplinary in nature, involving an understanding of biology, genetics, mathematics, statistics, economics, sociology, cultural anthropology, psychology, politics, geography, medicine, public health, ecology, etc.