Data
Charts
Charts turn a list of data into a picture so patterns are easy to see. In this section we read and interpret bar charts, dot plots, waffle diagrams and pie charts. Pie charts are new at this stage - they show the proportion of a whole.
Bar charts and dot plots
A bar chart uses bars whose height shows the frequency of each category or group. The taller the bar, the more common that value is. A dot plot stacks one dot for each item above its value on the number line. Count the dots in a column to read the frequency, and add columns to find totals or 'more than' amounts.
Waffle diagrams
A waffle diagram is a grid of squares. In a 100-square waffle each square is 1%, so the coloured squares show the percentage of each category. If 20 children are shown on 100 squares, each child fills 5 squares (5%). Always read the key to see what each colour means.
Pie charts
A pie chart is a circle split into sections. First find the total frequency, then divide the circle into that many equal parts. Each category takes as many parts as its frequency, so you can read its fraction or percentage of the whole. A key and a title tell you what the chart is about.
Choosing the right chart
Pick the chart that shows what you want to know. A bar chart or dot plot is best for comparing how many are in each category. A pie chart or waffle diagram is best for showing the proportion, fraction or percentage of a whole.
Worked examples
Reading a bar chart
- A grouped bar chart shows roses in bloom: 1-3 (3 bushes), 4-6 (8), 7-9 (12), 10-12 (6), 13-15 (9).
- To find the most common group, look for the tallest bar - the 7-9 group at 12.
- To find a total, add every bar: 3 + 8 + 12 + 6 + 9.
Answer: The 7-9 group is most common, and 38 bushes were looked at in total.
Reading a dot plot
- A dot plot shows test marks: 4 marks (1 child), 5 marks (2), 6 marks (4), 7 marks (3), 8 marks (2).
- To count 'more than 5 marks', add the columns for 6, 7 and 8 marks: 4 + 3 + 2.
- The highest score is where the dots stop, at 8 marks.
Answer: 9 children scored more than 5 marks, and the highest score was 8.
Reading a waffle diagram
- 20 children each chose a sport on a 100-square waffle diagram, so each child fills 5 squares (5%).
- Table tennis was chosen by 3 children.
- Percentage = 3 x 5% and squares = 3 x 5.
Answer: Table tennis is 15%, filling 15 squares.
Reading a pie chart
- Asif's pie chart of how 10 friends travel shows: walk 5, car 1, bus 3, cycle 1.
- The total is 10, so each friend is 1/10 of the circle.
- Walk is 5 out of 10, which simplifies to 1/2, and 1/2 is 50%.
Answer: Half of Asif's friends (50%) walk to school.
Choosing the right chart
- To show whether a candidate got more than 50% of the vote, you need to see part of a whole - a pie chart.
- To show which candidate got the most votes, you want to compare amounts quickly - a bar chart.
Answer: Use a pie chart for proportions and a bar chart for comparing amounts.
Where you see this in real life
- Reading a pie chart of a class's favourite films to see the most popular type.
- Using a waffle diagram to show what percentage of children chose each sport.
- Reading a bar chart of how many roses are in bloom on the bushes in a park.
Key words
- Bar chart
- A chart that uses bars whose heights show the frequency of each category or group.
- Dot plot
- A chart that stacks one dot for each item above its value.
- Waffle diagram
- A grid of squares where coloured squares show the percentage of each category.
- Pie chart
- A circle split into sections that shows the proportion of each category in the whole.
- Frequency
- How many times a value or category appears in the data.
- Key
- A guide that shows what each colour on a chart represents.