Pie Charts (Edexcel GCSE Statistics)

Pie Charts

What is a pie chart?

• A pie chart is a circle which is divided into slices (sectors) to show proportions

• They show the relative size of categories of data compared to each other

  • rather than their actual size or number

    • e.g. looking at the proportions of men and women working for a company, we might be more interested in the relative sizes of the groups than in the actual numbers of men and women

• There are 360° in a circle

  • We can use this to help us calculate the size of each slice of the pie chart

How do I draw a pie chart?

• This is shown easiest through an example

• The following data is collected for a class of 30 students about their favourite colour

• STEP 1
  Find the number of degrees that represents 1 student

  • There are 30 students in total, so 360° = 30 students

  • Divide both sides by 30, so 12° = 1 student

• STEP 2
  Calculate the angle for each category by finding a fraction of 360°

  • 11 students out of 30 said red was their favourite colour,

    • so this is

  • 4 students out of 30 said purple,

    • so this is

  • Repeat this for each category, they should sum to 360° in total

• STEP 3
  Draw the pie chart, using a protractor to measure the angles

  • Start by drawing a vertical line from the centre of the circle to the top ("12 o'clock")

  • Then use your protractor to measure the first angle and draw a line to this point

  • Move your protractor to this line, and repeat for the next category

  • Continue until the slices for all the categories are drawn

  • You should include a key or labels to show which slice represents which category

How do I interpret a pie chart or find missing information?

• It is easy to spot from a pie chart which category is the largest or smallest proportion

  • But you may be asked to do something more advanced like finding some missing information

  • Remember that all of the data is represented by 360°

• You can use the information you are given to find

  • how many degrees each person/piece of data is represented by

  • how many people/pieces of data 1 degree represents

• For example if you are told that there is a slice measuring 30° which represents 15 people

  •  30° = 15 people

    • 1° = 0.5 people (divide by 30)

    • 2° = 1 person (divide the first statement by 15, or double the second statement)

  • You can then use this information to help solve problems or find missing information