Interpreting results
Representing data
There is no single best chart ā only the best chart for THIS data and THIS question. Choosing well is half of presenting data properly.
Discrete and continuous data
DISCRETE data is counted in separate whole values: the number of pets, goals scored, students in a class. CONTINUOUS data is measured and can take any value in a range: height, temperature, time. This distinction drives the choice of chart. Bar charts suit discrete data; frequency diagrams suit continuous data.
The chart for the job
ā¢ Venn or Carroll diagram ā sorting things into groups with shared features. ā¢ Bar chart ā comparing discrete data. ā¢ Dual bar chart ā comparing TWO sets of discrete data. ā¢ Compound bar chart ā combining quantities into one bar to see parts AND totals. ā¢ Frequency diagram ā comparing continuous data. ā¢ Line graph ā how data changes OVER TIME. ā¢ Scatter graph ā comparing two sets of data points to look for a connection. ā¢ Pie chart ā the proportion each part is of the whole. ā¢ Infographic ā a quick, easily understood summary.
Justifying your choice
You are expected to JUSTIFY the chart you pick ā say why it suits the data. ā¢ Depth of snow at the end of every week ā LINE GRAPH, because it shows change over time. ā¢ Maths scores against science scores for 20 students ā SCATTER GRAPH, because you are looking for a connection between two sets. ā¢ Gold, silver and bronze medals for two countries ā DUAL BAR CHART, because you compare the bars side by side. 'It looks nice' is not a justification. 'It shows change over time' is.
Worked examples
Depth of snow at the end of every week
- The data is measured over time.
- A line graph shows change over time.
Answer: Line graph
Maths scores against science scores for 20 students
- Two sets of data, one point per student.
- You are looking for a connection.
Answer: Scatter graph
Gold, silver and bronze medals for two countries
- Two sets of discrete data to compare.
- Side-by-side bars make it easy.
Answer: Dual bar chart
The share of a class travelling by bus, car or on foot
- You want each part as a share of the whole.
Answer: Pie chart
Sorting shapes by 'has a right angle' and 'is red'
- Sorting by shared features.
Answer: Venn or Carroll diagram
Discrete or continuous: the height of 30 students
- Height is measured, not counted.
- It can take any value in a range.
Answer: Continuous
Where you see this in real life
- Newspapers pick line graphs for prices over time and pie charts for market share ā the same data, different questions.
- A weather app shows temperature as a line and rainfall chance as bars, because one is a trend and one is a comparison.
Key words
- Discrete data
- data counted in separate whole values
- Continuous data
- data measured, taking any value in a range
- Line graph
- a graph showing how data changes over time
- Scatter graph
- a graph comparing two sets of data points
- Justify
- give a reason for your choice