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Academic Skills Essentials: Math

Graphs

Graphs are an excellent way to display a lot of data in an effective manner, without having to write paragraphs of information. Different graphs are suited for different purposes and is important to know what type of graph to use to most efficiently show your results or support your argument.

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A pie chart is an easy way to display data and statistics that are part of a whole. Each part of the chart is relative to the size of a data category.undefined

  • Compare parts to the whole.
  • To show percentage or proportional data.
  • Best for 3 – 7 categories.
  • Good for marketing data.

Design notes:

  • Order slices according to size.
  • Add a key for each slice.

Make sure your values add up to 100%.

A bar chart shows data that can be sorted into categories. Each rectangular bar has a height proportional to the value of each category.

  • Compare numbers (frequency) in categories.
  • Can compare several categories of data.
  • Best for visualising data distribution for more than 3 categories.
  • Good for economics, statistics, marketing.

Design notes:

  • Use consistent colours.
  • Use horizontal labels to improve readability.

Start the y-axis at 0 to accurately reflect numbers.

A histogram shows continuous data (usually numbers). Histograms display a frequency distribution (shape) of a data set. undefined

  • Compare numbers (frequency) in intervals.
  • Summarises large data sets.
  • Good for statistics, business, economics.

Design notes:

  • As for bar chart.

Note there are no gaps between the bars (continuity of data).

A line graph displays data that changes continuously over time, creating a trend. Data points are connected with a line. undefined

  • Displays a trend over time (but time does not have to be one of the variables).
  • Can be used to make predictions based on data history.
  • Can be used to compare multiple variables, situations or information.

Design notes:

  • Use solid lines where possible.
  • Add a key.
  • Don’t plot more than four lines.

Adjust your axis so that your data takes up roughly 2/3 of the y-axis.

A scatter plot shows the relationship between two numerical variables, and how much one variable affects another. Time is not considered. The independent variable is always plotted on the x-axis. undefined

  • Can be used with a trend line or line of best fit to better show relationship and make predictions.
  • Good for statistics and most branches of science and engineering. 

 Design notes:

  • Use a maximum of two trend lines to improve readability.

Start the y-axis at 0 to accurately reflect numbers.

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How do I decide what type of graph to use?

  • Do I need to compare values? → pie chart; bar chart; histogram; line graph; scatter plot
  • Do I need to show the composition of my data? → pie chart
  • Do I need to show the distribution of my data? → bar chart; histogram; line graph; scatter plot
  • Do I need to analyse trends in my data? → histogram; line graph
  • Do I need to understand the relationship between my variables? → line graph; scatter plot

References

Oetting, J. (2018, March 20). Data Visualization 101: How to choose the right chart or graph for your data. Hubspot Marketing. https://blog.hubspot.com/marketing/types-of-graphs-for-data-visualization

Valcheva, S. (n.d.). Types of graphs and charts and their uses. Intellspot. http://www.intellspot.com/types-graphs-charts/