When we are working with data, we usually work with samples since it is too difficult, time consuming and expensive to work with population data. In fact, population data is not even required, and we can draw good conclusions from sampled data.
Population: Population is a group of items, units or subjects which is under the reference of study. Population may consist of finite or infinite number of units. Population is termed as universe by a number of statisticians and scientists.
Population can be classified in to four categories namely,
- Finite population
- Infinite population
- Real population
- Hypothetical population
(i) Finite population: If the number of items or units constituting the population is fixed and limited, it is known as finite population. For instance, the workers in a factory, students in a college, etc. This usually consists of existing items.
(ii) Infinite population: If the population consists of an infinite number of items, it is called an infinite population. For example, the population of all real numbers lying between 5 and 10; the population of stars in the sky, etc.
(iii) Real population: A population consisting of the items which are all present physically is termed as real population.
(iv) Hypothetical population: The population consists of the results of repeated trials is named as hypothetical population. The tossing of a coin repeatedly results into a hypothetical population of heads and tails, rolling of a die again and again gives rise to a hypothetical population of numbers from 1 to 6; etc.
Sample: A finite subset of statistical individuals in a population(S) is called a sample (s) and the number of elements in a sample s is denoted by n(s) and it is referred to as sample size.
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