### Introduction to pie charts

In benefit-risk communication, the slices on pie charts can represent the frequency or probability of different events. The extent to which each criterion contributes to the overall benefit-risk score may also be presented using pie charts. There are variants of a pie chart such as the Nightingale Rose or coxcomb and the doughnut chart. The popularity of pie charts in the mass media (see Spence 2005), and being part of school curriculum may make them suitable for many types of audiences.

Pie charts are made up of areas and angles to communicate part-to-whole information, where the entire circle (the 'pie') represents the denominator for the population and the slices represent the numerators for the different groups. However, there has been a long controversy about using pie charts due to the limit of visual perception (see Cleveland 1985 and Kosslyn 2006). Human visual perception simply could not handle area or angle comparison very easily or accurately (see Few 2009). Pie does not communicate precise data effectively (Kosslyn 2006), but numerical labelsmay be used.

Pie charts can be created easily in many software packages such as Stata, R, SAS, SPSS, Tableau, Spotfire, QlikView, IBM Many Eyes and Microsoft Excel. Microsoft Excel can also create doughnut chart easily. Nightingale rose can be created in software packages such as Microsoft Excel?, SAS, R, and Stata with some modifications to pie charts. The pie chart could be used interactively to display a risk for different individuals or subgroups.