The Four Major Statistical Scales of Measurement
1. Nominal or categorical
The nominal or categorical statistical scale of measurement is used to measure those variables that can be broken down into groups. Each group has attributes distinctly different from the other. The most commonly used nominal or categorical variables measured using this research scale of measurement are gender, civil status, nationality, or religion. These variables and their corresponding categories are as follows:
- gender – male or female
- civil status – single or married
- nationality – Filipino, Chinese, Singaporean, Malaysian, Indonesian, Vietnamese
- religion – Muslim, Christian, Buddhist, Shinto
Notice that the categories of each nominal variable do not indicate that one is superior or greater than the other. These are mainly classifications that separate one group from the other.
The nominal scale of measurement is referred to by statisticians as the crudest statistical scale of measurement. While this may be the crudest, this is a powerful statistical scale of measurement when correlating two nominal variables like gender and reproductive health bill position.
The statistical question in this instance is “Is there a correlation between gender and reproductive health position?” Chi-square is the appropriate statistical test for this question.
2. Ordinal
The ordinal statistical scale of measurement applies to variables that signify, as the root word suggests, “order” of the different groups. It is possible to rank order the different groups because each group shows attributes that are convincingly superior or greater than the other or vice-versa.
To illustrate this statistical scale simply and clearly, examples of variables that are measured using this scale of measurement are the following:
- order of child in the family – eldest, second eldest … youngest
- socioeconomic status of families – upper, middle, lower
- educational attainment – elementary, high school, college, graduate
- size – small, medium, large
Notice that while the different groups follow an order of magnitude, there is no discernible distance between them or that the distances could vary between each group. Say, the eldest child may be older by two years to the next eldest child, but the second eldest child may be three years older than the next child, and so on. No specific income difference describes the socioeconomic status, and so on. The number of years spent in the elementary is not the same as the number years in high school or the graduate school. The size difference between small, medium and large can vary widely.
3. Interval
The interval scale of measurement measures variables better than the rank order mode of the ordinal scale of measurement. There is now an equal spacing between the different groups that composes the variable. Examples of variables that can be measured using this statistical scale of measurement are the following:
- household income in PhP5,000 brackets – 1st group: earns up to PhP5,000, 2nd group: PhP10,000, 3rd group: PhP15,000
- temperature in 5 degree intervals – 5, 10, 15, 20
- number of student absences in one week – week 1 absence, week 2 absence, week 3 absence
- water volume in 5 milliliter increments – 5 ml, 10 ml, 15 ml, 20 ml
4. Ratio
The ratio scale of measurement works similarly with the interval scale. In fact, in using statistical tests, these two statistical scales of measurement are not treated differently from the other. The only difference between the ratio and the interval scale is that the former (i.e., the ratio scale) has an absolute zero point.
Examples of ratio variables are the following:
- weight in kilograms or pounds
- height in meters or feet
- distance of school from home
- amount of money spent during vacation