6.2 Pie charts: Activities

To see what we mean, you should follow our calculation of a pie chart using the data in Table 8.

1. Collect the data so the number per category can be counted. Table 8 shows the data.

2. Decide on a clear title.

   Title: ‘1992 Illinois population by race (thousands)’.

3. Decide on the total number of responses.

   The number of categories is four (the four races).

4. Calculate the degree share in each category.

As an example, here is the calculation of the degree share for African-Americans:

The degree share for each category is shown in Table 9.

Alternatively, you could calculate the percentage share of each category. Percentage share is calculated as follows (for the share of African-Americans):

If you are working by hand, it is best to work to the nearest whole number because it is hard to be more accurate than this when drawing. Make a final check that the number of degrees adds up to 360, then draw the pie chart (Figure 13). If you are using a computer to draw the chart, the raw data will be enough and the computer will do the calculation for you.

Figure 13: 1992 Illinois population by race (thousands)

What do you think Figure 14 shows us?

Now you can try drawing up a pie chart for yourself from the information below.

The Retail Price Index (RPI) is a UK index that looks at the expenditure habits and costs in the UK of a ‘basket’ of goods. The basket contains all the consumer goods that an ‘average’ household can expect to buy over time, 600 in total. Two groups of households are excluded from this, to make it more representative: pensioners and the high earners. 120 000 measurements are taken each month. The index is calculated monthly, and you may be aware of it as the basis for the monthly headline inflation rate.

The 600 consumer goods are split into areas of general consumption, such as food or housing. Table 10 shows some data on the relative expenditure of an ‘average’ household on goods in the housing sector of the basket. The relative expenditure on each of these goods is expressed in terms of a weight. So, for example, Table 10 shows that in 1998, in the ‘average’ household, three times as much was spent on council tax and rates as was spent on repairs and maintenance. As can be seen from the table, these weights change from year to year as expenditure changes. This is just a part of the data from the RPI.

Using the steps we have shown you, try to draw a pie chart using the 1998 data.