What's covered
Key facts
Bar charts, line graphs, population pyramids and choropleth maps
A bar line (vertical line) chart displays discrete data such as counts.
Box plots
The box runs from the lower quartile to the upper quartile, so its length is the interquartile range and it holds the middle 50% of the data.
Choosing and misleading representations
3D representations can distort the sizes of parts, so they should be interpreted with care and avoided when drawing charts.
Frequency polygons and cumulative frequency
A cumulative frequency graph can never have a negative gradient: it only rises or stays level.
Histograms and frequency density
In a histogram the area of each bar represents the frequency, not its height.
Pie charts and comparative pie charts
A common error is to find the angle as 360 divided by the frequency.
Stem and leaf diagrams
A back-to-back stem and leaf diagram shows two data sets either side of one shared stem so they can be compared.
Tables, tallies, pictograms and grouping data
Students are expected to know class width: the difference between the upper and lower boundaries of a class interval.
Bar charts, line graphs, population pyramids and choropleth maps
A choropleth map classifies the data for each region into classes and shades each region by its class.
Box plots
Box plots are compared using the medians (average) and interquartile ranges (spread), interpreted in context.
Practice questions with answers
A taste of the 81 questions in this topic, answers marked. Sign up to practise the full set with spaced repetition.
Which chart is best for comparing two groups' frequencies category by category?
- •A cumulative frequency graph
- ✓A dual bar chart
- •A single pie chart
- •A stem and leaf diagram
Which five values are needed to draw a box plot?
- •Lower quartile, mean, upper quartile, range, mode
- ✓Lowest, lower quartile, median, upper quartile, highest
- •Lowest, mean, median, mode, highest
- •Mean, mode, median, range, interquartile range
A bar chart of house sales has a vertical axis starting at 2000. Why is it misleading?
- ✓Differences between bars look bigger than they are
- •Differences between bars look smaller than they are
- •The bars no longer show the categories
- •The total of all sales is hidden
Where are points plotted on a cumulative frequency graph for grouped data?
- •At the class width of each group
- •At the lower class boundary of each group
- •At the midpoint of each group
- ✓At the upper class boundary of each group
Which kind of data is a histogram designed to display?
- •Discrete counts shown as single lines
- ✓Grouped continuous numerical data
- •Paired values of two variables
- •Qualitative data in named categories
What does a single pie chart show most clearly?
- ✓How a total is shared into proportions
- •How a variable changes over time
- •The exact frequency of each category
- •The spread of a numerical variable
Three minutes a day. Knowledge that sticks.
Practise all 81 Representing data questions with spaced repetition, so what you revise today is still there in the exam. Free to use, no card needed.