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Frequency distributions may be shown by tables or graphs. Use bar charts for categorical or quantitative discrete variables, histograms for continuous variables, and dot plots (especially useful for small data sets) for discrete or continuous variables.

By observing the frequency distribution of a categorical or quantitative variable, several shapes may be detected:

 When values or classes have similar percentages, the distribution is said to be fairly uniform. In a fairly uniform distribution there are no values or classes predominant over the others (a).

 When there is one value or class predominant over the others, the distribution is said to be nonuniform and unimodal with one peak (b).

 When there is more than one value or class predominant over the others, the distribution is said to be nonuniform and multimodal with more than one peak (c).

The value or class with the highest frequency is the mode of the distribution (see Figure 1.2).

Figure 1.2 Shapes of distributions.