Class Information

Some of the most frequent tasks of statistical data analysis are the classification (categorization) of observations and the interpretation of classified data. The classification in its simplest form is based on the assignment of a class number (or, in more general form, of a class property) to each observation.

As an alternative to a dedicated storage vector (red region in the figure above) the class information may equally well be stored as a normal variable of the data matrix. This brings the benefit that class information (if coded in numerical form) can be used for calculations and can directly influence, for example, the color coding of results. On the other hand class information as part of the data matrix includes the risk of mixing up class information with explanatory variables, which may pose problems in certain circumstances.

Displaying classified data

When displaying classified data we can distinguish three basic types:

• the depiction of count data in form of histograms or pie charts,
• the representation of the data in dependence of the corresponding class, and
• the coloring of the data points according to the class information.