12.6 Graphing two qualitative variables
The relationship between two qualitative variables can be explored using:
Many variations of these graphs are possible.
As an example, a study of road kill (Russell et al. 2009) produced the data in Table 12.3. There are two qualitative variables: the season (ordinal, with four levels) and the sex (nominal, with three levels including ‘Unknown’).
12.6.1 Stacked bar charts
The data can be graphed by using a bar for each season, stacking the bars by sex on top of each other, within each season (Fig. 12.22).
12.6.2 Side-by-side bar charts
Instead of stacking the bars within each season on top of each other, the bars can be placed side-by-side within each season (Fig. 12.23).
12.6.3 Dot charts
Instead of bars, dots (or other symbols) can be used in place of a side-by-side bar chart (Fig. 12.24).
12.6.4 Other variations
Many variations of these bar charts are possible. We can choose:
- horizontal or vertical bars;
- percentages or counts;
- stacked bar charts, side-by-side bar charts, or dot charts;
- either the sex of the possum or the season as the first division of the data.