The most commonly used measurement scales are: (i) Nominal scale; (ii) Ordinal scale; (iii) Interval scale; and (iv) Ratio scale.
(i) Nominal scale: In this scale, symbols, events or attributes are numbered in order to identify them. The number order is symbolic and not quantitative it is just convenient labels. Nominal scales are convenient ways to track people, objects and events. Although the nominal scale is the least powerful measurement level, yet it is very useful and is used in routinely in surveys and ex-post-facto researches for classification of major sub-groups of the population.
(ii) Ordinal scale: The ordinal scale measures degrees of separation between an event, object or emotion rather than quantitative measurement. The scale measures qualitative phenomena, and rank from highest to lowest. Ordinal measures have absolute values, and the real differences between adjacent ranks may not be equal. The usage of an ordinal scale implies ‘greater than’ or ‘less than’ without our being able to state how much greater or less. Measures of statistical significance are restricted to non-parametric methods.
(iii) Interval scale: In interval scale, the intervals in the scale are not fixed by zero but are adjusted as assumptions. Interval scales have an arbitrary zero. The Fahrenheit scale and time can be examples of an interval scale.
(iv) Ratio scale: Ratio scales are those scales of measurement which have an absolute or true zero of measurement. The various examples of ratio scale are Mass, length, duration,energy etc. A ratio scale has equal distances and a true zero.