Ratio is the fourth scale of measurement. It is considered to be the best among all the four scales of measurement as it satisfies all the properties needed for a perfect scale i.e. each value on this scale has a unique meaning, all the values on this scale can be arranged in proper order, the interval among its different values can be accurately measured and it has absolute zero, there is no value below zero on this scale. Weight is a simple example of this scale. It has unique values ; the interval between any two values of it can be easily and accurately measured; and zero weight means no weight. Similarly height is another example of ratio. Still another example is scores on a particular test. Here each score represents unique value; the interval among different scores can be precisely calculated; and zero score means no score. Ratio is the most powerful scale of measurement as various powerful statistical tools can be easily applied on it. You can best understand this scale by comparing it with the other three scales of measurement: nominal, ordinal and interval.
