There are four measurement scales (or types of data) to categorize different types of variables: nominal, ordinal, interval and ratio.

Ratio data has not only the properties of interval data but also “×” and “÷”. Ratio data has an absolute zero, below that there are not negative values. Good examples of ratio variables include height and weight. For instance, the height of A is 160cm and the height of B is 200cm. We can not only say B is 40cm taller than A but also that B’s height is 1.25 times as A’s. Zero is meaningful, referring no height.