An aggregate of objects (animate or inanimate) under study is called population or universe. It is thus a collection of individuals or of their attributes (qualities) or of results of operations which can be numerically specified.
A universe containing a finite number of individuals or members is called a finite inverse. For example, the universe of the weights of students in a particular class.
A universe with infinite number of members is known as an infinite universe. For example, the universe of pressures at various points in the atmosphere.
In some cases, we may be even ignorant whether or not a particular universe is infinite, for example, the universe of stars.
The universe of concrete objects is an existent universe. The collection of all possible ways in which a specified event can happen is called a hypothetical universe. The universe of heads and tails obtained by tossing a coin an infinite number of times (provided that it does not wear out) is a hypothetical one.
The statistician is often confronted with the problem of discussing a universe of which he cannot examine every member, i.e., of which complete enumeration is impracticable. For example, if we want to have an idea of the average per capita income of the people of a country, enumeration of every earning individual in the country is a very difficult task. Naturally, the question arises: What can be said about a universe of...
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