Principles of Data Science - Second Edition

The four levels of data

It is generally understood that a specific characteristic (feature/column) of structured data can be broken down into one of four levels of data. The levels are as follows:

• The nominal level
• The ordinal level
• The interval level
• The ratio level

As we move down the list, we gain more structure and, therefore, more returns from our analysis. Each level comes with its own accepted practice in measuring the center of the data. We usually think of the mean/average as being an acceptable form of a center. However, this is only true for a specific type of data.

The nominal level

The first level of data, the nominal level, consists of data that is described purely by name or category. Basic examples include gender, nationality, species, ...