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Using & Analyzing Graphs to Support an Essay

Instructor: Lisa Kuchta

Lisa has a master's degree in communication, has taught college communication and writing courses, and has authored a textbook on presentation skills.

Learn the basics of graphs and how to understand them. Also, learn how to use graphs in your own essays, including how to decide when to use graphs, which types to use, and how to best format them.

When to Use Graphs

Have you ever finished reading a paragraph full of dense information and, at the end of it, thought, 'What did I just read?' For me, and for many others, that happens after reading paragraphs full of numbers. Yes, your audience can comprehend that the 5 million earned in the second quarter is more than the 4.7 million earned in the first quarter, and that the 6 million earned in the third quarter far outweighs the 4.5 million earned in the fourth quarter. But the takeaway points are more easily lost upon your reader when they can only see the numbers in paragraph forms (without looking back, do you remember which quarters were the most and least profitable?). Here's a simple fact: when you have a lot of numbers to share with your readers, those numbers are often best served in a visual format. That visual format is a graph.

Types of Graphs and Their Purposes

If you explore your spreadsheet or word-processing program on your computer, you will see that there are a lot of options for charts and graphs. Let's explore the three most popular kinds of graphs that you might use and discuss how to understand them:

1. Line Graph - A line graph displays data over a period of time. For instance, if we were to put our previous example of quarterly earnings into a graph, it could be a line graph, like the one shown below. If you wanted to compare more than one company's earnings, you could add more lines to the graph (one for each company).

Line Graph

A line graph contains both an x-axis (the horizontal base) and a y-axis (the vertical spine). The x-axis is generally used to mark the passage of time - in the example above, the four quarters of the year. The y-axis represents what the data measures (e.g., money, customer reviews, approval ratings, etc.). You'll notice in the example above, that the scale (that is, the range of numbers) on the y-axis does not start at 0. Since graphs only need to show the relevant data, it is not always necessary that the axes show all potential numbers. Be sure to always read the numbers along both axes carefully to be sure you understand the data completely. A quick glance at the line graph might have led you to believe that Company B made no money in the first quarter because its line starting on the x-axis, but a closer read of the y-axis would show you that they actually made 4 million dollars.

2. Bar Graph - A bar graph is used to demonstrate comparisons among different categories at a singular time. So, if you wanted to examine current customer ratings of different products, a bar graph would be ideal to do that.

Bar Graph

A bar graph also uses x- and y-axes, but since the passage of time is not being recorded, the x-axis instead serves as the baseline for the bars. Always read the category labels for each bar to be able to understand the data. Again, the y-axis does not need to begin or end at a certain number, so read the range of numbers appropriately.

3. Pie Chart - A pie chart is a circle divided into different slices so that it resembles a pie. Pie charts should only be used when the pieces of data represent parts of a whole. For instance, if you were to ask your friends and family what their favorite flavor of ice cream is (and everyone could only choose one flavor), you could use a pie chart to represent the results. To use a pie chart, all pieces of data must be represented only once. So, in your ice-cream survey, if you had someone who chose chocolate and vanilla, you could not mark them in both categories; you would have to make them choose just one, or put them in the 'other' category.

Pie Graph

There are no x- or y-axes in pie charts, since all the data is contained in the circular form. The most important feature of a pie chart is the relative size difference between the different pie pieces. Ensure that you read the graph's title and labels fully to understand what data the pie slices are intended to represent.

Formatting Tips for Graphs

If you are creating a graph to use in your own essay and you have selected the most appropriate type, you should then take care to ensure that you format it in a way that makes it easy for your readers to understand and digest. Here are some tips you can follow:

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