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Ordinal Variable.
A variable whose possible values can be arranged in some order, such as short, medium, long . In contrast, a variable whose possible values are India, China, USA, are not ordinal variables. Arithmetic with the possible values of an ordinal variable does not necessarily make sense, but it does make sense to say that one possible value is larger than another.

Random Variable.
A random variable denotes possible outcomes of a random experiment.

Random Experiment.
A random experiment is the one in which all outcomes have equal chance of appearing. e.g A throw of fair dice has outcomes 1,2,3,4,5,6. Since all outcomes have an equal chance of appearing, throw of a fair dice is an random experiment and if x denotes the outcomes 1,2,3,4,5,6 then x is a random variable.

When the measurements are affected by the judgment of the data collector or data analyst rather than by standard statistical procedures, bias is said to be introduced. A biased estimate gives the value, which is different from the truth. Numerical value of bias is the average difference between the measurement value and the actual value which could have been obtained without bias. Unbiased or random selection procedure is without any bias.

Dependent Variable.
When value of the first variable is governed by the value of the second variable then first variable is dependent variable.

Independent Variable.
When value of the variable is not governed by the value of any other variable then such variable is called as independent variable.