The scale of measurement is a logical tool through which it is possibile measure a statistical unit. There are two types of scale of measurement:
- For a qualitative variable:
• nominal scale: differentiates between items based only on their names and other qualitative classifications they belong to, characterized by a absence of pre-established order. Hair color is an example.
• ordinal scale: whose attributes are incresing or descending order. The ordinal type allows for rank order (1st, 2nd, 3rd, etc.) by which data can be sorted, but still does not allow for relative degree of difference between them. Military hierarchy is an example.
- For a quantitative variable:
• interval scale: allows for the degree of difference between items, but not the ratio between them. Examples include temperature measurement, or percentage such as a percentage of faults ( Celsius and Fahrenheit temperature ).
• ratio scale: is a variable that assumes numerical values that allow comparisons both for difference and for the relationship between the modality that the units assume. Ratios are now meaningful because having a non-arbitrary zero point makes it meaningful to say, for example, that one object has “twice the length” of another (= is “twice as long”). Examples include mass, length, duration, plane angle, energy and electric charge.
Statistics Lessons Blog 