Comparing pie charts
Two or more pie charts can be used to compare two sets of data where the categories are the same or similar but there is a change in another variable, such as time or age. In such cases it is helpful to maintain the same ordering and colouring of slices in the second pie chart as the first in order to facilitate comparison. This may mean that in the second pie chart the slices are no longer presented in order of magnitude. If the two charts represent different sized totals show this by making the areas of the pie chart proportional to the totals they each represent.