Explainer: Bar Graphs

In this explainer, we will learn how to display and analyze bar graphs to answer questions.

Suppose we did a survey to find the favorite fruit of each student in a class. We might summarize the data in a table like the one below.

BananaAppleOrangeStrawberryKiwiGrapes
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From the table, we can see that four students chose oranges as their favorite fruit. Sometimes, using a table to represent our data is really useful. However, often it does not really give us a clear picture of what is going on. A better way is to represent it visually; this can be done using a bar graph, also sometimes called a bar chart. Let us draw a bar graph using the fruit preferences data.

The first thing we should do is draw our axes. We can label the horizontal axis with the different kinds of fruit. And on the vertical axis we put the number of students. To choose what number to start our vertical axis from and what number to finish with, we look for the highest and lowest numbers in our table. In this case, the highest is 10 and the lowest is 1. So, if we start our vertical axis at the minimum possible value, which is zero, and choose, say, 12 for the maximum, we will cover the whole range of our data.

Note that, in this case, our categories are types of fruit and we can put these on the horizontal axis in any order we like.

Now let us begin to fill in the bar graph. To help make sure our bars will be the correct heights, we draw in some horizontal grid lines, or ruled lines across from the vertical axis. If we begin at the left, with the Banana category, we know that 6 students chose bananas as their favorite fruit. So counting up to 6 on the vertical axis (marked in pink), this is the height of our first bar. The bar can be drawn above the Banana label on the horizontal up to a height of 6.

Continuing in this way for the rest of the fruit categories, we can complete our bar chart.

Notice that for the Apple category, the height of the bar is midway between 4 and 6, since 5 students chose apples as their preferred fruit, and similarly for Kiwi (3, between 2 and 4) and Grapes (1, between 0 and 2). We can see quite clearly from the bar graph that the most popular fruit (the one with the highest bar) was strawberries and the least popular (the one with the shortest bar) was grapes.

The bars in a bar graph do not all have to be the same color. Sometimes we use a different color to highlight important features as long as they are the correct height and the same width for each category. So, for example, we could have colored our Fruit bar chart as follows.