Explain the term 'Population' as it is used in Statistics. Define (a) Univariate, (b) Bivariate and (c) Multivariate population.

In common language the word 'population' means the number of persons living in a certain region. We may count the number of persons and obtain the size of population of that region. Similarly, we may find the population of certain animals in forests in a country or the population of certain plants in a garden and so on. The term population implies 'head count'.

However, in Statistics, the data on any single variable, or a set of variables, for all individual units in a region, constitute the population of that variable, or variables.

Univariate : If the data are on a single variable, the set of measurements constitutes a univariate population of that variable. We have a bivariate or multivariate population of the set variables. For example, we may have a univariate population of prices, or a population of incomes. We may have a bivariate population of height and weights of all individuals in a region.
Multivariate : A multivariate population of expenditures on various items of consumption of all households.