A variable (usually denoted by letters or symbols) is a characteristic, number, or quantity that takes different values in different situations.
A random variable is a variable which takes any value at random from all of the possible outcomes of an experiment. There are two types of random variable, discrete and continuous.
Note: A non-random variable is a variable which is not random.
The main types of variables include: independent, dependent, qualitative, quantitative, discrete and continuous.
Independent Variable |
Dependent Variable |
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|---|---|---|
Definition |
A variable is independent if it may vary freely and does not depend upon changes in other variables. It is usually denoted by $x$. |
A variable is dependent if it varies according to changes in other variables. It is usually denoted by $y$. |
Example |
Time spent revising for an exam. |
The marks from an exam. |
Example |
How many spoonfuls of sugar you put in your tea. |
How sweet your tea is. |
Qualitative Variable |
Quantitative Variable |
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|---|---|---|
Definition |
A variable is qualitative if it can not be represented by a number. |
A variable is quantitative if it can be represented by a number. |
Example |
The head of department's hair colour. |
The number of lecturers with brown hair. |
Example |
How students travel to university. |
The number of students that walk to university. |
Discrete Variable |
Continuous Variable |
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|---|---|---|
Definition |
A variable is discrete if it may take only a countable number of distinct values such as $0$, $1$, $2$, $3$, $4$, $\ldots$ If a variable can take only a finite number of distinct values, then it must be discrete. |
A variable is continuous if it can take any value within a finite or infinite interval. |
Example |
The number of people in your family. |
The combined weight of your family. |
Example |
The number of students on your course. |
The time your lecture lasted. |