Leaving out one or more of the parts of the whole.
Pie charts, or circle graphs as they are sometimes known, are very different from the other three types of graphs that we've looked at. They don't use a set of axes to plot points. In addition, they don't work with the same type of data that the other three work with. Pie charts are display percentages. Therefore, they are used to compare different parts of the same whole.
The circle of a pie graph represents 100%. Each portion that takes up space within the circle stands for a part of that 100%. In this way, it is possible to see how something is divided among different groups.
It is important to be aware of how pie charts can be misrepresented. There are two ways that this can happen:
Leaving out one or more of the parts of the whole.
Not defining what the whole stands for.
If a part of the whole is left out, then it increases the percent values of the other parts that are displayed. If a whole is not defined, then we do not know what the parts represent.