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1 2.6 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 3 is a bar chart which shows how the percentages of people with home access to the internet have changed between 1998 and 2004.

Figure 3
Figure 3 UK Households with home access to the Internet, April to June (source: National Statistics Survey, 2004)

Activity 7 (exploratory)

Study the bar chart in Figure 3. What do you think it shows about the growth in home access to the internet?

Answer

The first thing I 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.

My 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 I choose the bar for 1998 and look at the value on the vertical axis, I can see that it is just under 10%, so I 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 I estimate that 52% of households in the UK had access to the internet at home in 2004.

Activity 8 (exploratory)

Use the bar chart in Figure 3 to answer the following questions:

  1. What percentage of households in the UK had access to the internet at home in 2001?

  2. By how many percentage points did home access increase between 1998 and 2001?

  3. By how many percentage points did home access increase between 2001 and 2004?

Answer

  1. The bar for 2001 reaches to just under 40% on the vertical axis. I would estimate the value as 39%.

  2. To find the increase, we subtract the value for 1998 (9%) from that for 2001 (39%). This gives an increase of 30 percentage points.

  3. To find the increase, we subtract the value for 2001 (39%) from that for 2004 (52%). This gives 13 percentage points.

The solutions to the questions in Activity 8 confirm my initial impression (Activity 7) about the way in which home access to the internet has increased. Home access increased by more percentage points between 1998 and 2001 than between 2001 and 2004. So, although home access is still increasing, it does not seem to have been increasing as rapidly since 2001.