What Is a Bar Graph?
What are bar graphs? How do you make them? And what are they useful for?
Jason Marshall, PhD
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What Is a Bar Graph?
Successfully communicating information to others can be tough, which is why humans have invented all kinds of tools to help us out. Sometimes we use words, drawings, and even wild gesticulations to convey ideas. Sometimes we use music, alarms, birdcalls, and a whole host of other sounds to express things. And sometimes—in particular when talking about quantitative information—we use numbers, charts, and graphs.
Since this is the Math Dude, I’m going to leave it to Grammar Girl to talk about words and the Public Speaker to talk about all of those (hopefully not too wild) gesticulations. Instead, we’re going to focus on exploring the various ways that people convey quantitative information using charts and graphs. Over the next few weeks, we’re going to talk about the various types of graphs, how to make them, and what we can learn from them.
Today, we’re kicking things off by taking a look at the simple yet very capable bar graph.
What Is a Bar Graph?
You might not know it, but I’d hazard to guess that pretty much everybody in the modern world has seen one or two (or ten) bar graphs (also commonly known as bar charts) in their lives. One of the most common uses of bar graphs is to display the A/B/C/D/F grades of students in a class. You remember those kinds of charts, right? There are five bars of different heights labeled A, B, C, D, and F. And the height of each of these bars indicates the number of students in the class with each grade. They look like this:
Bar graphs can be used to represent lots of other information as well. In fact, pretty much any time you have quantitative data about something that’s broken down into several groups or categories (such as grade letters), you can make a bar graph to display the information. For example, TV news will often show the results of Yes/No surveys using very simple bar graphs showing the number of “Yes” and “No” responses. Or, during the run up to an election, you might see a bar graph in which each bar shows the percentage of support for each of a number of candidates.
And on and on and on—looking around, you’ll see bar graphs all over the place. And you’ll see that this very simple type of graph is very effective at conveying certain types of numerical information.
How to Make a Bar Graph
But before we get into a discussion of exactly what bar graphs are good at conveying, let’s spend a few minutes talking about the basics of constructing a bar graph. In truth, the noble bar graph is a pretty simple hombre to make, but let’s go over the basics just to make sure we’re all on the same page.
The height of each bar must be scaled to show its correct size relative to all the other bars.
A good first step to making a bar graph is to organize your data into a table. In the case of the grades of a class of students, the table would simply contain five columns—with the number of students earning each of the five letter grades in the columns. Once you have your data organized in such a fashion, you can go ahead and draw your bars. The only thing you have to keep in mind when drawing a bar graph is that the height of each bar must be scaled to show its correct size relative to all the other bars. Normally you’ll see a label beneath each bar telling you what category the bar represents, and you’ll see a vertical scale telling you how high each bar is. In the case of student grades, the vertical scale will mark the number of students in the class earning that grade.
When making a bar graph, it’s traditional to leave a bit of space between the various bars. This isn’t a super-important detail, but it will help distinguish these simple bar graphs from some of the other similar-looking graphs we’ll be talking about later. One final note: the bars in a bar graph don’t have to be vertical; if it strikes your fancy (or for some reason makes it easier to read), you can also draw all of the bars horizontal with the label on the left and the scale increasing to the right.
What Can We Learn From Bar Graph?
So that’s how to make bar graphs, now the big question is why might you bother to do so in the first place. After all, doesn’t a simple table contain the exact same information? Indeed it does, and sometimes a table is a perfectly fine way of communicating data to somebody.
Turning a table of data into a bar graph can help bring it to life.
But turning a table of data into a bar graph can help bring it to life. In most instances, it nearly immediately makes the relationships between categories clearer than a table alone. In fact, almost every time you’re interested in discussing the relative sizes of different categories, you’re better off making a bar graph since the diagram will allow you to directly (visually!) compare the categories to each other. If you don’t believe me, make up a fake table of student grades and then turn it into a bar graph. Once you’ve done that, ask yourself if the bar graph makes the overall distribution of grades easier to interpret and digest. I certainly think it does, and it’s one of the reasons that the simple bar graph should be a go-to tool anytime you need to present data that can be broken down into groups.
Bar Graphs and Histograms
Those of you who’ve been paying close attention may remember my mention of something called a histogram that came up when we talked about stem-and-leaf plots. At that time, I mentioned that the histogram is often a more convenient means of looking at the distribution or “shape” of data. Some of you might think that this sounds awfully similar to the main benefit of bar graphs that I’ve been touting. And you’d be right!
Because as we’ll see next time, bar graphs and histograms are very close cousins. And both are extremely useful tools for communicating quantitative information to others.
Wrap Up
OK, that’s all the math we have time for today.
For more fun with math, please check out my book, The Math Dude’s Quick and Dirty Guide to Algebra. And remember to become a fan of The Math Dude on Facebook, where you’ll find lots of great math posted throughout the week. If you’re on Twitter, please follow me there, too.
Until next time, this is Jason Marshall with The Math Dude’s Quick and Dirty Tips to Make Math Easier. Thanks for reading, math fans!
Bar graph image from Shutterstock.
About the Author
Jason Marshall is the author of The Math Dude’s Quick and Dirty Guide to Algebra. He provides clear explanations of math terms and principles, and his simple tricks for solving basic algebra problems will have even the most math-phobic person looking forward to working out whatever math problem comes their way.