Measurement System Analysis (MSA)





Validate the measurement system used to collect the data and quantify the:

  1. Process variation
  2. Appraiser variation

and the total measurement system variation.






Accuracy / Bias


For best accuracy of the data:


2) Record the data at the time it occurs.





Accuracy versus PrecisionAccuracy versus Precision

Resolution / Discrimination






To address a resolution issue try acquiring a larger samples size with the goal that some of these may create new observations or measurements.

Measure to as much resolution as possible and practical.















I Chart

Gage R&R

Variable Gage R&R





Four Criteria in Variable Gage R&R


1) % Study Variation is based on standard deviation
2) % Tolerance is based on USL and LSL
3) % Contribution is based on variance
4) The number of distinct categories based on process variation


Variable Gage R&R Criteria

2) % Tolerance



5.15 Study Variation = 99% (constant)



Calculating % Tolerance in Variable Gage R&R study



With the tolerance being 25, then:

Percent Tolerance Example Second Part




To optimize reproducibility in ATTRIBUTE Gage R&R:



To optimize reproducibility in VARIABLE Gage R&R:












MSA - Gage R&R Process Example

The picture below is shown to help illustrate how the assessment process can be done for a Gage R&R for either an Attribute or Variable MSA.

In this case, 30 bolts are randomly placed on a number. Before the process starts a team assigned a Master (Known) value or assessment for each of the bolts. In other words, each bolt is already known to be a PASS or FAIL.

In this case it is an Attribute MSA and the Master values are PASS or FAIL for each bolt. 

Each bolt is identified on the bottom with a PASS or FAIL indicator; however, the appraisers are not aware of these markings. 

NOTE: This could also be a Variable MSA if the goal was to assess the length or diameter of the bolts. 

There are 3 appraisers.

Each appraiser will make an decision (PASS or FAIL) on each bolt two times. 

Each time, the person coordinating the MSA will move the bolts around to a different number to randomize the assessment. This helps ensure the appraiser does not remember how they assessed a bolt the previous round. This is absolutely critical to remove bias (use randomization) from the assessment. 

The results are recorded carefully onto a spreadsheet from which the Six Sigma Project Manager will begin the Measurement System Analysis. 

The Six Sigma Project Manager will be evaluating three areas:

1) Comparing each appraiser to the Master values

2) Comparing each appraiser results to the other appraiser results. This is the "among" variation. 

3) Comparing each appraisers results to themselves. In other words the "within" variation. How were the results from Round 1 compared to their own Round 2 results. 

If the MSA is perfect, that means all appraisers agreed with the Master values on both rounds and they all agreed with the other appraisers both rounds, and they matched their own assessments each round. 

Interpreting the MSA results

The questions below help examine the extreme outcomes to demonstrate the main points and provoke thoughts and ways to consider all the data that is generated from a MSA. Understanding these situations will help understand more complicated and the nearly infinite number of outcomes that can occur within these extremes. 

What if all appraisers decided that one bolt PASSED while the master value was FAIL? This brings into the question of the Master values...are they actually correct? And if they are all correct, then all appraisers in need of additional training on the criteria to assess an acceptable part for an unacceptable part.

What if all appraisers decided that one bolt FAILED while the master value was PASS? Same response as above.

What if one of the appraisers doesn't match their own decisions on any of the previous round decisions? That appraiser is inconsistent and is not using the same criteria (whether objective or subjective) in making an assessment. This could be helped by clearer instructions, definitions or discipline by the appraiser to adhere to the instructions.

What if one of the appraisers matches all of their own readings on both rounds? Excellent. that appraiser is consistent within him/her self. But does the consistency match the Master values?

Building on the previous question, but what if none of the readings match the Master value? The person is consistent (precise) but not at all accurate. This likely is going to require additional training and back to the basics. 

Attribute Gage R&R Example One


Attribute Gage R&R Evaluation

Attribute Gage R&R Example Two

Take a look at the results below and make decisions on how to proceed. There is a lot of valuable information here, they key is interpreting it correctly and making improvements if needed. 

There were 3 appraisers, a set of Master values (called the Standard), and each appraiser made 2 randomized assessments of each part as PASS or FAIL.

Evaluating the "Within Appraiser" section, Appraiser 1 matched all the his/her readings on both assessments and Appraise 2 had two instances out of 30 trials that did not match.... so what are your thoughts?

Appraiser 2 should get some additional training right....well not necessarily. What if all of Appraiser 2 reading matched the standard (Master values)? 

Looking at the next section "Each Appraiser vs Standard", notice the only 25 / 30 readings matched the standard from Appraiser 2. So, 5 parts were assessed incorrectly compared to the Master values. This could either be a PASS decision when the standard was FAIL or vice versa.

One takeaway is that Appraiser 2 could use additional training or the Work Instruction could be improved to make it clearer as how to proper assess a good part from a bad part.

From the "Between Appraisers" section, notice that 24 / 30 readings matched each other across all two trials. That brings the lower level of the Confidence Interval down to 61.4%. 

Depending on how critical this assessment is or how critical the bolts applications is, generally you would like 29/30 where all assessments (>95%) match each other, each assessor repeats the same response on both trials, and they match the Master value. 

This MSA does not pass

The team should come up with improvements to make the assessment process more effective. This could include visual aids, actual good and bad parts for the appraisers to study, discussions with the customer, more detailed work instructions, discussions among all the appraisers. 

Once all the improvements are done, another Gage R&R should be done to prove the results. This is where it can get very time consuming and this is where a MSA can become a project within your project. Consult your Master Black Belt if the MSA continues to be a roadblock. This is one of the top Project Pitfalls to watch out for as a GB/BB. 

Variable Gage R&R Example


Variable Gage R&R Evaluation



MSA Training Download






The variation can be distinguished between four categories:

1) Appraisers (those that are measuring)

2) Parts or item being measured

3) Interaction of Appraisers and Parts

4) Replication error from the gauge

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