Click here to view a video on how histograms are made using SPC for Excel

Our SPC software, SPC for Excel, easily constructs and updates histograms based on data in an Excel spreadsheet. A histogram is a bar chart that provides a snapshot in time of the variation in a process. It tells us how often a value or range of values occurred in a given time frame. A histogram will tell us the most frequently occurring value (the mode), the overall range, and the shape of the distribution (e.g., bell-shaped, skewed, bimodal, etc.). It is best to have 50 to 100 data points to construct a histogram, if possible. This program will construct a histogram from the raw data. It will automatically determine the number of classes (bars) as well as the class width. The options available in our SPC software are given below. These include the opportunity to change the number of classes, the class width, and the starting lower bound.

For more information on histograms, please see our December 2005 and January 2006 newsletters on histograms on our website. We also offer a histogram training module in PowerPoint that you can easily customize.

Histogram Options

• Adding descriptive statistics
• Changing the number of classes
• Changing where the histogram begins (lower bound)
• Changing the width of the classes
• Viewing the frequency distributions
• Easy updating of an existing histogram when new data is entered

If you select the option to display the descriptive statistics, the software will produce a box to the right of the histogram (as shown above) with the following information:

• Mean
• Standard Error
• Median
• Standard Deviation
• Variance
• Sum
• Count
• Maximum
• Minimum
• Range
• Kurtosis
• Skewness

If you want to change the number of classes, where the histogram starts or the width of the classes, select the classes button in the upper left hand part of the histogram and you will get the following input form with your options:

You can view the frequency distribution by selecting the "Freq. Dist" button on the histogram. The frequency distribution for this histogram is shown below.