Ordinal data is data where there are labels, and there is a meaningful ordering between the labels. For example, consider asking people to rate their happiness, with choices of Unhappy, Somewhat happy, and Happy. If we asked five people to rate their happiness, we might get the data: Happy, Unhappy, Somewhat happy, Happy, Unhappy.
In addition to all the comparisons we were able to perform with the nominal data:
- We can make relative comparisons. For example, persons 1 and 4 are equally happy (based on the data) and both are happier than persons 2, three, and 5.
- When we have two variables that are both ordinal, we can compute nonparametric correlations between these variables.
- We can summarize variables based on their median. For example, the median level of happiness in this data is Somewhat happy.
Ordinal data is sometimes referred to as being ordered categorical.
Often ordinal data is assumed to be either nominal or interval when performing data analysis. This is because more powerful techniques have been developed for these measurement scales.