The image shows a bar graph about the favorite seasons of the boys and girls in a class. The blue represents the fall, the red represents the winter, the green represents the spring and the purple represents the fall. At a glance, you can see that the favorite season among the girls is summer and the boys is fall. The least favorite season for both girls and boys is winter. On the left side of the graph are numbers that represent how many students were surveyed. Numbers of students are represented on the x axis and the y axis shows the genders.
When interpreting a bar chart, look at the tallest bar and look at the shortest bar. Look at the titles, look for inconsistencies and ask why they are there.
Types of Bar Graphs
Single: Single bar graphs are used to convey the discrete value of the item for each category shown on the opposing axis. An example would be a representation of the number of males in grades 4-6 for each of the years 1995 - 2010. The actual number (discrete value) could be represented by a bar sized to scale with the scale appearing on the x axis. The Y axis would show a tick and label for the corresponding year for each bar.
Grouped A grouped or clustered bar graph is used to represent discrete values for more than one item that share the same category. An example would be, using the single bar example above and introduce the number of female students in grades 4-6 for the same categories, years 1995- 2010. The two bars would be grouped together, side by side, and each could be color coded to make it clear which bar represents male vs. female discrete value.
Stacked: Some bar graphs have the bar divided into subparts that represent the discrete value for items that represent a portion of a whole group. An example would be to represent the actual grade data for males in each grade 4-6 and then scale each grade discrete value as a part of the whole for each bar. Again color coding would be needed to make the graph readable.
Once you've had some experience with bar graphs, you'll want to check into the many other graphs that mathematicians and staticians use. Bar graphs are used in school as early as kindergarten and they are seen in the curriclum through to high school. Graphs and charts are the standard in visually representing data. If a picture is worth a thousand words then you'll appreciate the value or interpreting information presented in bar charts and graphs. More often than not, I tend to use a spreadsheet to represent data in bar charts. The tutorial here is helpful to learn how to use a spreadsheet to create a bar chart or graph.