Data Levels of Measurement

A variable has one of four different levels of measurement: Nominal, Ordinal, Interval, or Ratio. (Interval and Ratio variables are sometimes called Continuous or Scale). Therefore, the researcher must understand these levels, as they, along with the phrasing of the research question, determine the appropriate statistical analysis.

Four Different Levels of Measurement

In descending order of precision:

Nominal–Latin for name only (Republican, Democrat, Green, Libertarian)

Ordinal–Think ordered levels or ranks (small–8oz, medium–12oz, large–32oz)

Interval–Equal intervals among levels (1 dollar to 2 dollars is the same interval as 88 dollars to 89 dollars)

Ratio–Let the “o” in ratio remind you of a zero in the scale (Day 0, day 1, day 2, day 3, …).

The first level of measurement is nominal. At this level, the numbers in the variable simply classify the data. Additionally, you can use words, letters, and alpha-numeric symbols. For example, suppose there are data about people belonging to three different gender categories. In this case, the person belonging to the female gender could be classified as F, the person belonging to the male gender could be classified as M, and transgendered classified as T.  This type of assigning classification is nominal level of measurement.

The second level of measurement is ordinal. This level depicts some ordered relationship among the variable’s observations.  Suppose a student scores the highest grade of 100 in the class.  In this case, he would be assigned the first rank.  Then, another classmate scores the second highest grade of an 92; she would be assigned the second rank.  A third student scores an 81, so the system assigns them the third rank, and so on.  The ordinal level indicates an ordering of the measurements.

The third level of measurement is interval.  The interval level classifies, orders, and ensures equal distances between intervals on the scale. For example, an interval level of measurement, such as anxiety scores between 10-11 and 40-41, represents equal intervals. A common example is Celsius, where the distance between 94°C and 96°C is the same as between 100°C and 102°C.