## Try This - Reading a chart

Diagrams are a common graphical way of representing information. Processes and ideas can often be summarised more effectively in diagrammatic form than in words.

As a learner you need to be comfortable with reading graphical information. You also need to learn how to read diagrams in the sense of extracting information from them and interpreting what they mean.

A chart is a type of diagram used to summarise large amounts of numerical information in a graphical form. Charts also provide a useful way of showing relationships between different values.

You will come across different types of chart, such as line graphs, histograms, pie charts and bar charts. They are used for different purposes. In the remainder of this study tool we shall focus on bar charts.

In a bar chart, information is represented by a series of bars of different heights or lengths. A bar chart has two axes, and labels on each tell us about the information being represented.

Figure 1 is a bar chart which shows how the percentages of people with home access to the internet have changed between 1998 and 2004.

### Have a go!

Study the bar chart in Figure 1. What do you think it shows about the growth in home access to the internet?

### What’s the answer?

The first thing you will have noticed is that the bars are getting longer from left to right, so access to the internet increased during the period represented. However, the ‘jumps' between the bars in the first few years seem to be larger than those for the later years. An interpretation of this is that there was more rapid growth in internet access in those earlier years.

Although charts present information in a graphical form so that it can be grasped quickly, it is important to look carefully at a chart. You should look at the chart's title and the labels on the vertical and horizontal axes. Then pick one of the bars and work out what it represents.

The vertical axis of the chart in Figure 3 is labelled ‘Percentages'. The values on the vertical axis go from 0 to 60 in intervals of 10 (0, 10, 20, 30 and so on); note that the fact that the vertical axis only goes up to 60 can make the percentages seem higher than they really are. The horizontal axis is labelled from 1998 through to 2004. Each bar represents data for one year from 1998 to 2004.

If you look at the bar for 1998 and look at the value on the vertical axis, you can see that it is just under 10%, so can estimate that 9% of UK households had access to the internet at home in 1998. The bar for 2004 reaches a little over the 50% mark, so you can estimate that 52% of households in the UK had access to the internet at home in 2004.

### Try this:

Use the bar chart in Figure 1 to answer the following questions:

- What percentage of households in the UK had access to the internet at home in 2001?
- By how many percentage points did home access increase between 1998 and 2001?
- By how many percentage points did home access increase between 2001 and 2004?

### What are the answers?

- The bar for 2001 reaches to just under 40% on the vertical axis. So you would estimate the value as 39%.
- To find the increase, we subtract the value for 1998 (9%) from that for 2001 (39%). This gives an increase of 30 percentage points.
- To find the increase, we subtract the value for 2001 (39%) from that for 2004 (52%). This gives 13 percentage points.