The level of measurement refers to the relationship among the values that are assigned to the attributes for a variable. Ordinal - Again this is a set of categories, but these categories can be ranked in a meaningful order. Though ordinal scales can be ranked or ordered, the distance between points varies. With nominal and ordinal measures, the mode can be a helpful measure of central tendency . We find the same distance between each possible value.
Examples are number of children, age, and test scores.
These variables have a distinct and meaningful zero-point. Examples are temperature or distance measurements. In order to take advantage of more powerful statistical methods that can not be used at the categorical-nominal level, however, we assign a numeric value to these categories. Statistics is mostly the manipulation of numbers. Names are not numbers.