Also Known As
Frequency Distribution

A histogram graphically demonstrates the frequency with which various values of a particular variable occur in a set of data. The height of the bar indicates the frequency of occurrence.


To quickly and easily demonstrate a data set's distribution.

To compare two time periods, looking for changes.

How do I use this tool?

Note: A histogram can easily be constructed using most spreadsheet software. If you prefer to create one by hand, use the following procedure.

1. From the raw numbers (the data), DETERMINE THE RANGE by finding the highest and lowest values (generally on the y-axis).

2. DETERMINE THE NUMBER OF BARS that will be used. Bars represent the group of "things" being counted or measured. Be aware that problems with the pattern may arise if there are too few or to many bars used in the histogram.

3. DETERMINE THE WIDTH of each bar. (Generally on the x-axis)

4. CREATE A COMPILATION TABLE and fill in the values for each grouping (bar).


6. DRAW THE BARS, they should correspond to the values from your table in step 4.

7. IDENTIFY AND CLASSIFY the pattern and distribution of the data set.

Expertise Required
This tool is easy to use and requires little or no training.
Recommended Supplies/Materials
Spreadsheet software

Provides quick summary of lots of data.

Is easy to construct with spreadsheet software.

Allows rapid visualization of the center and variation of the distribution, in addition to a distribution's shape.


Does not provide a difinitive indication of a normal distribution.

Where can I go to learn more?

Bauer J, Duffy G, Westcott R. Improvement tools. The quality improvement handbook. 2nd ed. Milwaukee, WI: ASQ Quality Press; 2006. p. 109-48.

American Society for Quality. Data collection and analysis tools: histogram. 2009 [cited 2009 July 28]; Available from: http://www.asq.org/learn-about-quality/data-collection-analysis-tools/overview/histogram.html

University Research Co. LLC. Health care improvement project: histogram. 2008 [cited 2009 July 28];