Pie Charts

Definition:

A Pie Chart is a type of graph that displays data in a circular format, where sections (or ‘slices’) of the pie represent different categories within a dataset.

Pie charts are primarily used to compare parts of a whole.
They depict proportions and percentages, which makes them useful in visually representing statistical data.

The first step is to calculate the total frequency, or the sum of all the individual frequencies. Treat this as the ‘whole’ or ‘total’.
Each sector of the pie chart represents a category of data. The size of the sector (the ‘slice’ of the pie) is proportional to the amount of data in that category.
Calculate the angle for each pie slice by using the formula: (frequency/total frequency) x 360.
Accurately measure and draw these angles on your pie chart with a protractor.

Observe the size of each slice to understand the proportion of the whole that it represents.
Pie charts may include labels or a key, so remember to refer to these for a precise understanding of the data being represented.
Remember that all the slices together represent 100% of the data.

Not suitable for comparing more than five or six categories because it becomes difficult to tell the sections apart.
Not appropriate for datasets where categories have similar frequencies as it becomes hard to distinguish the differences visually.
Percentages in a pie chart must total 100% — they are less useful for depicting data where categories could overlap or when data doesn’t add up to a meaningful whole.

The sum of angles in a pie chart should always equal 360 degrees.
Always label each sector clearly.
It’s a good practice to start the first category on the right, drawing the angle anti-clockwise.
Keep categories organised in a logical or ordered manner, such as highest to lowest frequency.
If there are many categories with small frequencies, combine them into an ‘Other’ category to make the chart easier to understand.