Presenting Data: How to Communicate Your Message Effectively

Chapter 3Charts (bar charts, histograms, pie charts, graphs)

Many charts presenting data display a wrong or inappropriate message. This can be either because of the poor presentation via scale differences or truncation or because the data are not represented well. This chapter will look at the rationale for charts, show through examples why certain charts are not good and illustrate how we can simply improve some charts with a little thought. User perception plays a large part in understanding charts, and illustrations of how the wrong message can be taken from charts are shown.

3.1 How the user interprets charts

When a user is shown a chart, the most usual approach is to seek to understand the visual display of the data without recourse to the axes, footnotes or other help that may have been available. So, if the chart does not represent the data well, the wrong message may be assimilated. We often make the presumption that the originator of a chart will understand the data and present the data within a chart in the way it should be interpreted. However, experience tells me that not only do newspapers present poorly designed and constructed charts but so do National Statistical Institutes.

The basic presumption of this chapter is that the chart's originator is trying to represent the data well and show a message from doing so. Otherwise, one has to ask why the chart has been included in a document. From some challenges I have put to originators, the answers as to why some ...