Graphing Qualitative Data

Bar Graphs

A graph made of bars whose heights represent the frequencies of respective categories is called a bar graph. The bar graphs for relative frequency and percentage distributions can be drawn simply by marking the relative frequencies or percentages, instead of the category frequencies, on the vertical axis.

Reproduced here, is Table 2.1 (from the previous page) for reference with Figures 2.1 and 2.2.

Job Description	Number Employed
Labourers	21
Mechanics	38
Filters	9
Clerks	12
Draughtsmen	4
Total	84

Fgure 2.1: Bar Graph for the Frequency Distribution of Table 2.1

Pie Charts

A circle divided into sectors that represent the relative frequencies or percentages of a population or a sample belonging to different categories is called a pie chart.

To construct a pie chart multiply 360 by the relative frequency for each category to obtain the degree measure or size of the angle for the corresponding category. Table 2.3 shows the calculation of angle sizes for various categories of table 2.2.

Table 2.3: Calculating Angle Sizes for the Pie Chart

Job Description	Relative Frequency	Angle Size
Labourers	0.25	360(0.25) = 90.0
Mechanics	0.45	360(0.45) = 162.0
Filters	0.11	360(0.11) = 39.6
Clerks	0.14	360(0.14) = 50.4
Draughtsmen	0.05	360 (0.05) = 18.0
Total	1.00	360

 
Figure 2.2:Pie Chart for Percentage Distribution of Work Force