Conducting GR&Rs

The key to a good GR&R study lies in the upfront planning. A GR&R study can be planned using the following 5 steps:

1. Define the objective of the study.
2. Define the components of the study.
3. Make the measurements.
4. Calculate the %GR&R.
5. Take action to improve the measurement process.

Step 1: Define the objective of the GR&R study:

• This step involves defining both what instrument (or family of instruments) will be studied as well as the product or product features to be studied.

Step 2: Define the components of the study:

• The components to consider include the people (testers or appraisers), the (test) method, the materials (or samples to test), the (testing) equipment, and the environment (such as conditioning requirements and the ambient temperature).

• Use 2 or 3 people who routinely conduct the test as the appraisers; do not replace the typical users with engineers or quality professionals.

• The test method used should be exactly as documented. Do not add new steps or precautions.

• Regarding test samples, if a non-destructive test will be used, at least 5 samples (and typically 10 samples) will be needed.

  • Be sure to use actual “production” parts.

  • Parts should be well marked.

• Ensure that the test equipment has adequate discrimination for the job. The equipment used should, of course, be the measuring device normally used without special repairs or adjustments.

• The environmental aspects of the study include taking into account special conditioning, temperature, and/or relative humidity considerations.

Step 3: Make the measurements:

• It is best for each appraiser to take all the measurements (including replicate measurements) for the study before having the next appraiser start taking measurements.

• The samples measured should be randomly selected and preferably “anonymous” to the appraiser to reduce bias.

Step 4: Calculate the %GR&R:

• This is the heart of the GR&R study. There are several techniques for calculating the %GR&R. Part of the planning involves deciding what type of analysis technique will be used.

• R&R Analysis techniques include:

  • Analysis for Non-Destructive Measurements
  • Analysis using ANOVA
  • Analysis for Destructive Measurements
  • Analysis for Attribute Measurements
  • Analysis Using Graphical Techniques

• The %GR&R will tell us if the measurement system is “good” or if it is “poor” and must be improved.

Step 5: Take action:

• If the measurement system is validated as “good,” additional action may not be necessary.

• If it is “poor,” action to improve the measurement system is needed.