ABSTRACT
In each of the situations we examined it was meaningful to calculate an average value. Clearly, it makes sense to speak of the mean yield, the mean impurity or the mean brightness of several batches of pigment. In many other situations we must deal with qualitative variables which cannot be averaged to produce a meaningful result. We might, for example, record whether a batch was made for export or for the home market. We might record that an employee was female or that she was located in the research department. Destination, sex and location are qualitative variables and when summarizing such variables it is useful to count and then to calculate proportions or percentages. We might speak of the proportion of batches made for export and to calculate this proportion we would need to count the total number of batches and the number made for export. We might also speak of the percentage of employees who are female or the proportion of staff located in the research department.
