5 Data Visualization
5.1 Using graphs

Knowing how to convey information graphically is important in presenting statistics. The following is a list of general rules to keep in mind when preparing graphs.

A good graph:

• accurately shows the facts,
• grabs the reader’s attention,
• complements or demonstrates arguments presented in the text,
• has a title and labels,
• is simple and uncluttered,
• shows data without altering the message of the data,
• clearly shows any trends or differences in the data,
• is visually accurate (i.e. if one chart value is 15 and another 30, then 30 should appear to be twice the size of 15).

Why use graphs to present data?

Because they…

• are quick and direct,
• highlight the most important facts,
• facilitate understanding of the data,
• can convince readers,
• can be easily remembered.

There are many different types of graphs that can be used to convey information, including:

• bar charts
• pictographs
• pie charts
• line charts
• scatterplots
• histograms

Knowing what type of graph or chart to use with what type of information is crucial. Depending on the nature of the variables, some types are more appropriate than others. For example, categorical variables like school subjects are best displayed in a bar chart or pie chart while continuous variables such as height are illustrated by a line chart or histogram.

Graphs: four guidelines

If you have decided that using a graph is the best method to relay your message, then there are four guidelines to remember:

1. Define your target audience
   Ask yourself the following questions to help you understand more about your audience and what their needs are:
   • Who is your target audience?
   • What do they know about the issue?
   • What do they expect to see?
   • What do they want to know?
   • How will they use the information?
2. Determine the message(s) to be transmitted
   Ask yourself the following questions to figure out what your message is and why it is important:
   • What do the data show?
   • Is there more than one main message?
   • What aspect of the message(s) should be highlighted?
   • Can all the messages be displayed in the same graph or chart?
3. Use appropriate terms to describe your graph
   Consider the following appropriate terms when labelling the graph or describing features of it in accompanying text:
   

   Table 5.1.1 Terms to describe graphs
   Table summary
   This table displays the results of Table 5.1.1 Terms to describe graphs. The information is grouped by If your graph... (appearing as row headers), Use the following terms... (appearing as column headers).

   If your graph...	Use the following terms...
   describes components	share of, percent of the, smallest, the majority of
   compares items	ranking, larger than, smaller than, equal to
   establishes a time series	change, rise, growth, increase, decrease, decline, fluctuation
   determines a frequency	range, concentration, most of, distribution of x and y by age
   analyses relationships between variables	increase with, decrease with, vary with, despite, correspond to, relate to

4. Experiment with different types of graphs and select the most appropriate
   • Pie chart (description of components)
   • Bar chart (comparison of items and relationships, time series, frequency distribution)
   • Line chart (time series and frequency distribution)
   • Scatterplot (analysis of relationships)