Chartjunk
As with bar charts, pie charts are often graphical representations of a small number of values. For example, a pie chart of the gender of students in a class is only based on a single value, the proportion of males. As a result, there is a temptation to 'enhance' pie charts as 3-dimensional objects — chartjunk.
Resist the temptation — it does not make the data any easier to understand and may indeed be misleading since 3-dimensional pie charts can over-emphasise the categories closest to the viewer.
Hospital workforce in Australia
Health administrators need to understand the composition of their workforce. The 3-dimensional pie chart below shows the occupations of employees in Australian hospitals in 2008.
The viewpoint distorts the visual impression given by the different categories. For example, the diagram incorrectly suggests that there were more Domestic and other staff than Administrative staff. Actually 15.5% were Administrative staff but only 13.2% were Domestic and other staff.
Small is beautiful
In general, it is better to draw a standard pie chart smaller rather than embellishing it with chartjunk.
Extra holidays?
A moderately large company with 426 employees, half of which are hourly paid, is considering organisational changes. Before implementing any new policies, all employees are given a questionnaire to assess their attitudes to various possible changes to the work environment.
Among the changes under consideration is an option for employees to take an extra day of vacation without pay each month. The 'exploded' pie chart below describes the responses to this idea.
The simpler small pie chart below shows the data more clearly.