Bar Graphs

Bar graphs are used to highlight separate quantities. They are useful for comparing quantities within or among categories. A bar graph can describe the relationship of several variables at once.

How much people tip

Source: Poretz and Sinrod, The First Really Important Survey of American Habits, 1989
Using the chart on the left, for example, you can compare how many people tip from 11-15% as opposed to over 20%. You can also compare the tipping habits of men vs. the tipping habits of women.

The bars in a bar chart can appear vertically as in the graph above, or horizontally as demonstrated below:

Source: U.S. Department of Education, National Center for Education Statistics, 1995-96 National Postsecondary Student Aid Study

A bar graph can show negative as well as positive quantities:

Average SAT Scores by Parental Education of Test Taker, 2001

Source: The College Board

The zero (0) line in this graph indicates the mean (i.e. average) scores on the 2001 SAT. The mean math score was 514 out of 800, and the verbal was 506. So each bar indicates how many points away from the mean all the test takers scored according to their parentsí level of education. Some students scored below the mean and some above. What does the information provided by the graph show? What is the main point?

A stacked bar graph adds some of the advantages of a circle graph: the graph displays the quantities, but it also shows the relative proportions of the categories to each other as well as to the whole.

Physicians By Sex and Age

Source: American Medical Association, 1999

We can see that the largest number of physicians fall into the 35-44 years old category (approximately 215,000).
And in every age category there are many more male physicians than female.
In which category is the difference between the number of male and female physicians least? greatest? Ans.

Another type of stacked bar graph shares other characteristics of a pie chart, but is able to present more comparisons:

Physicians by Sex and Selected Specialty

In this graph, the male-female ratio is broken down by medical specialties.
1) In which specialty do female doctors predominate? Ans.

2) Which specialty has the largest number of physicians? The fewest? Ans.

3) In which category are the numbers of male and female physicians most equal?Ans.

4) In which is the disparity greatest? Ans.

For practice on bar graphs exercises, click on the arrow below

To go on to line graphs, Click here

To go on to circle graphs, Click here