SPC Blog

What Do These Histograms Tell You?

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Bar Charts: Paretos and Histograms

Our previous blog introduced histograms. Histograms tell you four things about your process. Remember what those were? If not, see our previous blog, What is a Histogram? . Histograms also can give you insights to things you might not normally see. The example below demonstrates this.

Here is the background information for you. A supplier sends in weekly shipments of one raw material to you. There is one raw material characteristic that is key to how it performs in your process. The supplier provides you with a Certificate of Analysis with...

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histogram

What is a Histogram?

By
Bar Charts: Paretos and Histograms

A histogram is a snapshot in time of your process. It tells you four things:

  • Which result (or range of results) occurs most frequently
  • How much variation there is
  • What the shape of the variation looks like
  • If any results are out of specifications

Remember, all processes have variation. Processes in statistical control tend to form a stable pattern, which is called a distribution. Distributions are characterized by three parameters: location, spread, and shape. These parameters can be estimated from a histogram. An example of a...

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What is a Pareto Chart?

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Bar Charts: Paretos and Histograms

A Pareto chart helps you answer questions. What is the reason for the most rework or scrap in your organization? Which customers complain the most? What keeps us from getting the books closed after the end of the month. These questions are common in organizations, but we don’t always agree on the answer. This is where the Pareto chart comes in. A Pareto chart is a data-based approach to determining what “vital few” issues you should be working on.

The Pareto chart is named after Vilfredo Pareto, an Italian economist, who discovered that 80% of Italy’s wealth was held by 20% of the...

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The Basic EMP Study and Gage R&R [video]

The Basic EMP Study and Gage R&R [video]

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Measurement Systems Analysis

This is the final blog in a four-part series on Gage R&R studies. The first blog addressed what a gage R&R study is . The second blog addressed Gage R&R studies and process variation and determine the % of total variance due to the measurement system. The third blog examined how good your measurement system is using an Evaluating the Measurement Process (EMP) classification developed by Dr. Donald Wheeler. This blog provides a...

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hardness tester

How Good is My Measurement System?

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Measurement Systems Analysis

You just completed your ANOVA Gage R&R analysis. The results indicate that your measurement system is responsible for 40% of the process variance (GRR%). You look up the guidelines on the internet and this is what you see:

  • Less than 1%: The measurement system is acceptable.
  • Between 1% and 9%: The measurement system is acceptable depending on the application.
  • Greater than 9%: The measurement system is not acceptable and should be improved.

You are in trouble! 40% and it can’t be greater than 9%! What will your customer say? Should you...

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test method

Gage R&R and Process Variation

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Measurement Systems Analysis

This is the second in a four-part series on Gage R&R. The first blog explained what a Gage R&R study is . This blog examines the relationship between the Gage R&R results and the process variation and answers the question:

Is the measurement system capable of telling the difference between the parts or samples taken the process?

This is just another way of asking if the measurement system can be used to control the process. The basic equation describing the relationship between the...

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What is a Gage R&R Study?

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Measurement Systems Analysis

This is the first of a four-part blog on gage R&R. It answers this basic question:

What is a Gage R&R study?

If you google this question, you will get several answers including this one from the www.isixsigma.com dictionary:

“Gage R&R, which stands for gage repeatability and reproducibility, is a statistical tool that measures the amount of variation in the measurement system arising from the measurement device and the people taking the measurement.”

This statement is...

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What is the Purpose of a Control Chart?

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Control Charts

This is the third in a four-part series introducing control charts. The first blog addressed the question of what a control chart is. The second blog explored the relationship between variation and control charts . This blog begins to answer the following question:

What is the purpose of a control chart?

We will continue with the driving to work example shown in the last two blogs to explore three different purposes for a control chart....

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common and special causes on a control chart

Variation and Control Charts

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Control Charts

This is the second in a four-part series introducing control charts. The first blog addressed the question of what a control chart is . This blog will answer the following question:

What is variation and how does it relate to a control chart?

Understanding variation is the key to effectively using a control chart. A control chart provides a method for your process to communicate with you – to tell you if the process is doing what you designed it to do (only common causes of variation are...

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