WHAT IS IT?

A bar graph, also known as a histogram, the most commonly used graph, is a snapshot of the distribution of any set of data. It shows the actual number of times an event or issue occurs. The data are lined up according to frequency.  The strength of a bar graph is that it provides an easy-to-read picture of the location and variation in a data set.  The bar graph becomes an effective, practical working tool in the early stages of data analysis.

WHEN IS IT USED?

• When it is important to see the frequency of distribution of the data

• When there is a need to understand the amount of variation in any set of data

• When the data are numerical

• When it is necessary to see the shape of the data’s distribution

• When analyzing whether a process can meet the customer’s requirements

• When seeing whether a process change has occurred from one time period to another

• When determining whether the outputs of two or more processes are different

• When communicating the distribution of data quickly and easily to others

• When one needs to identify problems and opportunities for improvements

• When comparing one process (or group, department, class, grade, test, etc.) to another
   

1. Determine the process or system to be studied.

2. Select the class or subdivisions by which to display the data.

3. Record the data by class or subdivision.

4. Draw the bar graph with an X and Y axis.

5. Divide the X-axis into the number of classes or subdivisions and label each.

6. Scale the Y-axis from zero to the total number of data points in the class with the most frequency.

7. Draw the graph using the data.

8. Study the shape

9. Calculate the statistics

10. Compare the bar graph to the normal distribution