Graphs that Display Data Study Guide
Introduction to Graphs that Display Data
Errors using inadequate data are much less than using no data at all.
– Charles Babbage (1792–1871)
In this lesson, you will be visually introduced to the many graphs used to display data, including tables, bar graphs, line graphs, scatter plots, pie charts, pictographs, and stem-and-leaf plots.
Graphs are incredibly useful because they communicate information visually. You probably have read graphs in newspapers, magazines, online, or in the classroom. When complicated information is difficult to understand, an illustration—or graph—can help get your point across quickly.
Tables are used to organize information into columns and rows. Usually, a title of the data presented is located at the top of the table, and there may be descriptions or titles in the column heads or row heads. Before looking at the data, you should ask yourself "What is this table telling me?" By focusing on what the table tells you, you will be able to find the data that you need easier, and analyze it.
Bar graphs are easy to read and understand. Bar graphs can be used to present one type of data, or may contain different colored bars that allow for a side-by-side comparison of similar statistics.
When you read a bar graph, there are several things you must pay attention to—the title, two axes, and the bars.
The title gives an overview of the information being presented in the bar graph. The title is usually given at the top of the graph.
Each bar graph has two axes, which are labeled. The axes labels inform you what information is presented on each axis. One axis represents data groups; the other represents the frequency of the data groups.
The bars are rectangular blocks that can have their base at either the vertical axis or the horizontal axis. Each bar represents the data for one of the data groups.
Line graphs aren't as pretty to look at as bar graphs, but they are easy to read. Again, different types of data may be presented at the same time, as in the following case.
It may help you to think of a line graph as being formed by connecting the topmost points of vertical bars on a bar graph and then erasing the bars.
Line graphs are good to display information that continues, such as temperatures or snowfall.
Scatter plots have points scattered all over the place.
Like line graphs, scatter plots use horizontal and vertical axes to plot data points. However, scatter plots show how much one variable is affected by another.
Scatter plots usually consist of a large body of data. The closer the data points come when plotted to making a straight line, the higher the connection between the two variables, or the stronger the relationship.
If the data points make a straight line rising from left to right, then the variables have a positive correlation.
If the line goes from a high value on the left down to a right axis, the variables have a negative correlation.
Pie charts, or circle graphs, are a great way to "see" data. Pie charts represent a whole, or 100%, as shown in this one.
You can make some rough estimations regarding the different slices of the pie just by glancing at the chart. For example, if a slice is about a quarter of the pie, you can say "Hey, that's about 25%." Sometimes these charts are two-dimensional, and sometimes they are three-dimensional. As always, you should approach a chart wondering "What is this chart telling me?"
Instead of using lines, bars, or chunks of pie to represent data, pictographs use pictures. You may see these types of graphs in newspapers and magazines.
Pictographs are also sometimes called picture graphs or histograms. Each picture on a pictograph represents a quantity of something. There is a key to tell you what each picture means. Here is an example of a pictograph.
Stem-and-leaf plots are the least understandable of all the charts you have studied so far. In other words, if you never saw a stem-and-leaf plot before, it is hard to tell what one means. Look at the graphic.
A stem-and-leaf plot splits number data into a "stem" and a "leaf." The leaf is the last digits of the number and the other digits to the left of the leaf form the stem. The number 149 would be split as:
As you can see, the original value—149—can still be found.
Like scatter plots and pictographs, stem-and-leaf plots show the frequency with which certain things occur.
Find practice problems and solutions for these concepts at Graphs That Display Data Practice Questions.