Pie charts along with bar graphs are the most common types of graphical representation for qualitative data. It takes categorical data and breaks it down by group, showing the percentage of data points that fall into each group. Since a pie chart takes on a shape of a circle, the slices that represent each group can easily be compared and contrasted. Each data point in a pie chart must fall into one and only one category, and the sum of all slices should be 100% or close to it, subject to a bit of rounding error. Pie chart does not have to say how much each slice is, only what percentage it is of the total, although absolute values of slices and/or total are sometimes included as well.^[1,p.96] It is important to watch for totals when examining a pie chart from a survey. The percentages of the pie chart only apply to the people who were surveyed; how many the results mimic the population depends on many factors, one of which is sample size. Without knowing the sample size it is impossible to tell how accurate the information is^[1,pp.98-99] or which of several pie charts from several survey companies is the most reliable.

The following tips help to evaluate a pie chart for statistical correctness:^[1,p.100]

• Checking that the percentages of all slices add up to 100% or very close to it- any round-off error should be very small.
• The "Other" slice of the pie chart should not be larger than many other slices.
• The total number of units should be reported with the pie chart.
• Three-dimensional pie charts should be avoided. They don't show the slices in their proper proportions- the slices in front look larger than they should be.

Ideally, a pie chart should not have too many slices, because a large number of slices distracts the reader from the main point(s) the pie chart is trying to relay. However, lumping many small remaining categories into one slice of "Other" that together is one of the largest in the whole pie chart, leaves the readers wondering what's included in that particular slice.^[1,p.96]

Unlike a bar graph, with a pie chart the scale cannot be changed to over-emphasize or downplay the results. No matter how a pie chart is sliced up it is always a sliced up circle, and making the pie chart bigger or smaller does not change the relative proportions of the slices.^[1,p.105]