In statistics, A Random Variable is a set of possible values from a random experiment which is known in advance and the experiment can be repeated underer identical condition. According to Investopedia,
“A random variable is a variable whose value is unknown or a function that assigns values to each of an experiment’s outcomes.”
A random experiment is an experiment in which
- All possible outcomes of the experiment are known in advance.
- Any performance of the experiment results in an outcome that is not exactly known in advance.
- The experiment can be repeated under identical condition.
More precisely we can say that,
There is a rule that assigns a real number to each outcome (sample point) of a random experiment is called a random variable (r.v.). It is governed by a function of the variable. Hence, a it is a real-valued function X (x) of the elements of the simple space (omega) where x is an element of (omega). Further, the range of the variable will be a set of real values.
In tossing a coin, x =1, if the coin falls with head, and x= 0 if the coin falls with a tail. The height of persons can be given by X (x)= X, the height is measured in centimetres or inches. A random variable is usually denoted by any of the capital Latin letters X, Y, Z, U, V etc.
Different types of random variables
Generally, there are two types, namely
Discrete random variable
Say x is a variable, which can take a finite number of values in an interval of the domain, is called a discrete random variable. For example, if we toss a coin, the variable can take only two values 0 and 1 assigned to tail and head respectively, i.e.,
X(x)= 0(if x is tail) or 1(if x is head).
Let, A variable X, which can take any value in its domain or in an interval or the union of intervals on the real line, is called Continuous random variable. For a continuous variable, the probability of a point is zero, i.e., P (X = x) =0.
Properties of random variable
The properties are following,
- If X is a variable and a,b are any two constants, aX + b is also a random variable.
- If X is a variable, X square is also a variable.
- If X is a variable, 1/X is also a variable.
- If X and Y are two variables defined over the same space, X + Y, X -Y, aX, bY or aX + by are also random variables where a and b are any two constants except that a and b both are not zero.