The word population or statistical population is used for all the individuals or objects on which we have to make some study. We may be interested to know the quality of bulbs produced in a factory. The entire product of the factory in a certain period is called a population. We may be interested in the level of education in primary schools. All the children in the primary schools will make a population. The population may contain living or non-living things. The entire lot of anything under study is called population. All the fruit trees in a garden, all the patients in a hospital and all the cattle in a cattle form are examples of population in different studies.
A population is called finite if it is possible to count its individuals. It may also be called a countable population. The number of vehicles crossing a bridge every day, the number of births per years and the number of words in a book are finite populations. The number of units in a finite population is denoted by . Thus is the size of the population.
Sometimes it is not possible to count the units contained in the population. Such a population is called infinite or uncountable. Let us suppose that we want to examine whether a coin is true or not. We shall toss it a very large number of times to observe the number of heads. All the tosses will make an infinite or countable infinite population. The number of germs in the body of a patient of malaria is perhaps something which is uncountable.
Target and Sampled Population:
Suppose we have to make a study about the problems of the families living in rented houses is a certain big city. All the families living in rented houses are our target population. The entire target population may not be considered for the purpose of selecting a sample from the population. Some families may not be interested to be included in the sample. We may ignore some part of the target population to reduce the cost of study. The population out of which the sample is selected is called sampled population or studied population.