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**Introduction**

When secondary data are not available for the problem under study, a decision may be taken to correct primary data by using any appropriate method. The required information may also be obtained by the following methods, viz. census method, and sample method.

**Universe**

A universe, in statistics, refers to a population that comprises the units or the informants of the data whether animate or inanimate, relating to a problem under study. In other words, it is the totality of the phenomenon under study or the aggregate of the objects of a statistical investigation.

For instance, if we are to study the average expenditure made by the students of a certain college consisting of 5000 students, the universe, here, will be the ‘college’ consisting of all the 5000 students and the unit or the informant, in such a case will be each one of these 5000 students belonging to said college.

**Types of Universe**

Universe is of the following four types.

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**1.** Finite universe.

**2.** Infinite universe.

**3.** Existing universe.

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**4.** Experimental universe.

**Finite Infinite Existing Experimental**

**1.** **Finite Universe:**

Finite universe is one in which the number of units information is definite and limited. For example, the ‘college’ as cited above is a finite universe as in this case the number of the units of information i.e. the students is definite and limited i.e. 5000.

**2. Infinite universe:**

An infinite universe refers to a population in which the number of the units comprised therein cannot be definitely ascertained. For example, the population of stars in the sky, the population of temperatures at various points of the atmosphere, the population of heights, weights and ages of the people in a country are examples of infinite universe. Further, if a universe is very large, it is also regarded as an infinite universe such as the number of leaves on a tree.

**3. Existing Universe:**

An existing universe is one which already exists with all its units in the form of concrete objects. The investigator has nothing to do for its creation except its discovery and location. For instance, a college, a university, a library, a country, and a state consisting of its concrete objects like students, books, individuals respectively are examples of existing universe. Such a universe, also, may come either under a finite or under an infinite universe.

**4. Experimental universe:**

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An experimental universe is one which is constituted through experiments being conducted by an investigator and is not found already in existence. For example, a record made of the number of heads and tails got upward by tossing a coin for a number of times, say 100, 200 or 500 times is a case of experimental universe.

Similarly, a record made of the number of times of obtaining the number ‘5’ with the flipping of a dice for certain number of times is an example of experimental universe.

Here, the universe is not already in existence but is created by the investigator himself through his experiments for a number of times. An experimental universe is generally of infinite character as there is no limit to the number of times of experiments may be conducted for recording the happenings of a particular event.