ASQ — Seven Basic Quality Tools: The Check Sheet And The Histogram (1)

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This first article introduces the Check sheet and the Histogram, basic tools which are used to collect and analyze data and may be adapted for a wide variety of purposes.

This series of articles presents the 7 Basic Quality Tools for Process Improvement used in the field. These are defined as instruments or techniques to support and improve the activities of quality management and improvement. ASQ has made available to the members and the public a huge amount of information on the "quality" body of knowledge (BOK). It is only meant to be a starting point, but oh so useful.

1. Check Sheet

It is a simple data recording device, custom designed by the user, which allows them to readily interpret the results. Check sheets are often confused with checklists which are used to verify that steps have been completed. This structured, prepared form for collecting and analyzing data, can be used manually or adapted for automated collection.

When to Use a Check Sheet:

• When data can be observed and collected repeatedly by the same person or at the same location;
• When collecting data on the frequency or patterns of events, problems, defects, defect location, defect causes, or similar issues;
• When collecting data from a production process.

Check Sheet Example:

The figure below shows a check sheet used to collect data on the number and the type of telephone interruptions for each day of the week. The tick marks were added as data was collected over several weeks. Off-hand, we can rapidly see that there were more interruptions on Monday and Tuesday AND that they were mostly for Wrong numbers or from the Boss. Using simple arithmetic, we can calculate percentages. Depending on the objective of the study, for instance for a call desk, we would look at improving the form by defining the reasons and the time period.

2. Histogram

A frequency distribution shows how often each different value in a set of data occurs. The histogram is the most commonly used graph to show the frequency distributions and although it looks very much like a bar chart, there are important differences between them, the least of which is the calculations for grouping the information.

When to Use a Histogram:

• The data are numerical;
• You want to see the shape of the data’s distribution, especially when determining whether the output of a process is distributed approximately normally;
• Analyzing whether a process can meet the customer’s requirements;
• Analyzing what the output from a supplier’s process looks like;
• Seeing whether a process change has occurred from one time period to another;
• Determining whether the outputs of two or more processes are different;
• You wish to communicate the distribution of data quickly and easily to others.

How to Create a Histogram: Read the full article on preparing a histogram. Basically, you collect at least 50 consecutive data points from a process on a histogram worksheet to set up the data. This helps to determine the number of bars, the range of numbers that go into each bar, and the labels for the edges. After calculating W (Width, step 2 of the worksheet), you adjust it to a convenient number, and then place the numbers on a graph.

Histogram Analysis:

• Before drawing any conclusions from your histogram, be sure that the process was operating normally during the time period being studied. If any unusual events affected the process during the time period of the histogram, your analysis of the histogram shape likely cannot be generalized to all time periods.
• Typical distribution shapes of the histograms are: Normal; Skewed; Double-Peaked or Bimodal; Plateau or Multimodal; Edge Peak; Comb; Truncated or Heart-Cut; or, Dog Food. Their meaning is described here shapes and what they mean.
Resources:
♦ You can find a check sheet template to track up to 10 defects on each day of the week. This tool also creates a histogram, bar chart, and Pareto chart using the same check-sheet data.
♦ Use this link to get a simple, but powerful, histogram generating tool Histogram template (Excel) to analyze the frequency distribution of up to 200 data points.

§ This News post was adapted by J.P. Amiel, ASQ Senior, CQA ret., Web committee Chair, from content at ASQ's Quality Resources pages, which are excerpted and adapted from The Quality Toolbox, Second Edition, ASQ Quality Press.
ASQ References:

Here is a list of the articles in this series:

 Article Title ASQ — Seven Basic Quality Tools: The SeriesASQ — Basic (And Not So Basic) Quality Tools Resources ASQ — Seven Basic Quality Tools: The Check Sheet And The Histogram (1)ASQ — Seven Basic Quality Tools: The Pareto Chart (2)ASQ — Seven Basic Quality Tools: The Control Chart (3)ASQ — Seven Basic Quality Tools: The Fish Bone Diagram (4)ASQ — Seven Basic Quality Tools: The Scatter Diagram (5)ASQ — Seven Basic Quality Tools: Stratification (6)
News Montreal Section 07/01/2022 8:26am CDT