3.8 Pie charts and bar charts: summary

Two common display methods for data relating to a set of categories have been introduced in this section. In a pie chart, the number in each category is proportional to the angle subtended at the centre of the circular chart by the corresponding ‘slice’. In a bar chart, the number in each category is proportional to the length of the corresponding bar. The bars may be arranged vertically or horizontally, though it is conventional to draw them vertically where the labelling of the chart makes this practicable. You have seen that attempts to make pie charts and bar charts look ‘three-dimensional’ can make them considerably harder to interpret.