ABSTRACT
Categorical data consist of variables whose values comprise a set of discrete categories. Such data require different statistical and graphical methods than commonly used for quantitative data. A categorical variable is one for which the possible measured or assigned values consist of a discrete set of categories, which may be ordered or unordered. In the limiting case, only one table variable may be recorded or available, giving the categorical equivalent of univariate data. The representation of numerical magnitude and categorical grouping, and the apperception of patterns and their meaning, must be extracted from the visual display. In the limiting case, only one table variable may be recorded or available, giving the categorical equivalent of univariate data. Graphs carry the message home. A universal language, graphs convey information directly to the mind. “Categorical” means different things in different contexts. The chapter also presents an overview of the key concepts discussed in this book.
