Proportions within groups

To compare the distributions of a categorical variable in different groups, it is best to examine the proportions within the groups — the cell frequencies divided by their group totals.

The table below shows the work settings of all enrolled nurses in Australia in 1993, 1996 and 1999.

  Workplace  
Year  Hospitals  Aged homes Community   Other      Total   
1993 19,981 14,714 1,717 6,255 42,667
1996 20,367 11,899 1,571 4,860 38,697
1999 19,847 10,376 2,315 3,159 35,700

From the table of within-year percentages below, it is clearer that the percentage of nurses working in hospitals has increased and the percentage working in aged homes has decreased.

  Workplace  
Year  Hospitals  Aged homes Community    Other       Total   
1993 46.8 34.5 4.0 14.7 100.0
1996 52.6 30.7 4.1 12.6 100.0
1999 55.6 29.1 6.5 08.8 100.0

Bar charts of proportions

Bar charts can be used to graphically compare groups and it is again best to use proportions within groups rather than raw frequencies, especially if the groups are of different sizes.

Clustering the bars

Each cluster of bars above is a valid bar chart for one group. Alternatively, the same bars can be clustered by the variable of interest:

This makes it easier to make comparisons between the groups.