3.6 Pie Chart
i) Geometrically it can be seen that the area of a sector of a circle taken radially, is proportional to the angle at its center. It is therefore sufficient to draw angles at the center, proportional to the original figures. This will make the areas of the sector proportional to the basic figures.
For example, let the total be 1000 and one of the component be 200, then the angle will be
In general, angle of sector at the center corresponding to a component
ii) When a statistical phenomenon is composed of different
components which are numerous (say four or more components), bar
charts are not suitable to represent them because, under this situation,
they become very complex and their visual impressions are questioned.
A pie diagram is suitable for such situations. It is a circular
diagram which is a circle (pie) divided by the radii, into sectors
( like slices of a cake or pie ). The area of a sector is proportional
to the size of each component.
iii) As an example consider the yearly expenditure of a Mr. Ted, a college undergraduate.
Tuition fees $ 6000
Books and lab. $ 2000
Clothes / cleaning $ 2000
Room and boarding $ 12000
Transportation $ 3000
Insurance $ 1000
Sundry expenses $ 4000
Total expenditure = $ 30000
Now as explained above, we calculate the angles corresponding to various items (components).
Tuition fees =
Book and lab =
Clothes / cleaning =
Room and boarding =
Sundry expenses =