The distinction between types of variables is important because specific statistical measures can be applied to each category, as shown in the paragraphs that follow. Computations of proportions, percentages, ratios and rates are basic statistical procedures used in describing the categorical composition or distribution of qualitative variables and serve as useful tools for the standardization of the statistics compared. It is important to keep in mind that the measures of composition or distribution should not be calculated for small numbers of observations. In that case, actual numbers (absolute frequencies) should be preferred. A proportion is defined as the relative number of observations in a given category of a variable relative to the total number of observations for that variable. It is calculated as the number of observations in the given category divided by the total number of observations.