| A variable is any measurable characteristic or attribute that can have different values for different subjects. Height, age, amount of income, country of birth, grades obtained at school and type of housing are examples of variables.
Observation
An observation is a single piece of data about a variable
Independent variable
An independent variable is the variable whose values are independent of changes in the values of other variables. It its the variable deliberately controlled or changed to assess changes in the dependent variable.
Dependent variable
A dependent variable depends on the independent variable.
Categorical variables
Nominal variable
A nominal variable describes a name or category. For example, for the variable 'method of travel to school' all its values are words such as bus, walk, car and tram. Nominal variables are often referred to as categorical variables.
Ordinal variable
An ordinal variable is a number that represents a category. For example, postcodes and school year levels.
Numerical variables
A numerical variable is one that describes a numerically measured value. Numerical variables can be either discrete or continuous.
Continuous variable
A continuous variable is a numeric variable that can take any value within a certain range. For example, distance, age and temperature are continuous variables.
Discrete variable
A discrete variable can only take a finite number of values within a certain range. An example of a discrete variable is the number of children in a family – a family can have 0,1,2 or 3 children but not 2.5.
Class interval
A class interval is a group of data values for a variable. The intervals are generally the same size – for example, 4-6, 7-9 and 10-12. However, the intervals may have different sizes such as 4-6, 7-9 and 10-14. The boundaries of class intervals must not overlap so that each observation can be allocated to only one interval. | 
