Radar graphs
A radar chart is a graphical method of displaying multivariate data (e.g. different features of an item, time periods etc). These graphs look a bit like spider webs, with each variable represented by spokes (called radii) starting from the same point and spread out in a circle.
A line is drawn connecting the data values for each radii so it looks like a star. This helps us identify the frequency of each observations and whether there are any outliers.
Worked example
Example 1
The annual sales per $1000$1000 units of two products are shown in the following radar chart.
(a) How many units of Product B were sold in November?
Think: Where is the Product B's red dot for November on the graph?
Do: The red dot for November is on the $6$6, which means $6000$6000 units of Product B were sold in November
(b) How many more units of Product A were sold in June than Product B?
Think: This time we're going to look at the difference between the blue dot and red dot for the June spoke.
Do: The blue dot is on the $10$10 and the red dot is on the $3$3, this is a difference of $7$7, so $7000$7000 more units of Product A were sold in June than Product B.
Practice question
Question 1
The annual sales of two products are shown in the following radar chart.
How many units of Product B were sold in March?
$\editable{}$
How many units of Product A were sold in November?
$\editable{}$
How many units of Product A were sold throughout the entire year?
Pareto charts
A Pareto chart is used to identify the most significant factors in a set of categorical data. The chart combines a column graph and a line graph, and has two vertical axes, one for each graph type.
- The columns represent the frequency for each category, or factor in a process, but could also represent cost, or some other unit of measurement. The columns are arranged in descending order, from tallest on the left to shortest on the right (i.e. most significant to least significant). The value for each column is read from the left vertical axis.
- The line graph or polygon represents the cumulative percentage of the values for each column. It always curves upwards, but decreases in steepness, from left to right. The value of any point on the line graph is read from the right vertical axis.
Practice question
Question 2
Bill caught the train and noted what activity each person in his carriage (excluding himself) was doing between the next two stops. The Pareto chart shows the results.
How many other people were in the carriage? You can assume that each bar is either in line with a tick on the left-hand $y$y-axis, or exactly halfway between ticks.
Using the bar section of the Pareto chart, find the percentage of people on the carriage (excluding Bill) that make up the three most common activities. You can assume that each bar is either in line with a tick on the left-hand $y$y-axis, or exactly halfway between ticks.
Round your answer to the nearest percentage.
Other graphs
The ability to effectively interpret graphs comes with exposure to many different styles of graphs and an interest in deciphering the information included. Look for articles on topics that interest you and analyse any data or graphs given. The investigation: Choice of graph for data has suggestions for visual essays which include a wide range of different types of graphs over many interesting topics. Look carefully at scales included and ask what information is trying to be conveyed. For example, is there information given in absolute frequencies, relative frequencies (frequencies written as percentages), cumulative frequencies (frequencies added up over time or categories).