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Gage R&R Methodology

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  • Lesson resourcesResources
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About this lesson

This lesson describes a step by step process for planning and conducting a Gage R&R Study. It includes templates for data collection for both variable data studies and attribute data studies.

Exercise files

Download this lesson’s related exercise files.

Gage R&R Methodology
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Gage R&R Methodology - Solution
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Quick reference

Gage R&R Methodology

There is a recommended process for conducting a Gage R&R study. This methodology guides the study manager through the steps to a successful conclusion.

When to use

Whenever planning a Gage R&R study, use the planning and executing methodologies. 

Instructions

A Gage R&R Study is a process just like most other business activities. As such, there is a best practice methodology that should be followed to maximize the effectiveness and minimize the cost and business disruption to the business. The process can be divided into three phases:

  • Planning – this involves focusing the study, designing the study and then coordinating for all the resources needed to conduct the study.
  • Data collection – this is the phase in which data items are measured and data is recorded for analysis.
  • Analysis – this phase determines the level of repeatability and reproducibility. This phase is quite different depending upon whether the data is variable data or attribute data.

For our purposes, we have divided this methodology into two parts – planning and executing.

Planning

  1. Identify the measurement that is to be investigated – this limits and focuses the study.
  2. Identify the measurement approach used for this measurement – this further limits and focuses the study. If no system is currently in use, one needs to be developed so the Gage R&R becomes part of the validation of that new system.
  3. Design the study (# appraisers, # items, # replicate trials, location and environment).
  4. Communicate the plan – inform stakeholders of upcoming activities and their participation requirements.
  5. Coordinate the resources – availability of appraisers, creation of the sample items to be measured, access to the measurement equipment, other needed support.
  6. Train appraisers if required.

The results of the study design and planning are often captured in the data collection form. These forms are very different depending upon whether the measurement is comprised of variable data or attribute data. If using a statistical software application such as Minitab, it will design the study and create the data collection form. If doing the analysis manually, the form is normally created in a spreadsheet application such as Microsoft Excel. A unique feature about the attribute data collection is that you can choose to include a reference standard for each item and that allows additional calculations for Miss Rate, False Alarm Rate, and Effectiveness.

Example:

Variable data – 3 appraisers, 10 items, 3 replicate trials

Attribute data – 3 appraisers, 30 items, 2 replicate trials.

Hints & tips

  • It is very easy to confuse the items once they have been randomized for measurement. Be sure to keep track of which is which and record data correctly.
  • Using an application like Minitab makes this process go very quickly and smoothly.
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  • 00:04 Hi, I'm Ray Sheen.
  • 00:06 Let's continue our discussion of Gage R&R by looking at the step by
  • 00:10 step approach for planning and conducting a Gage R&R study.
  • 00:16 I'll start with an overview of the three phases of a Gage R&R study.
  • 00:20 The first phase is the planning phase.
  • 00:23 The keys to this are to focus the study, create the plan and
  • 00:27 then make your preparations.
  • 00:29 While the third of these, sounds the simplest,
  • 00:31 I actually find it the most difficult because of the work to create items for
  • 00:35 measurement and lining up the resources.
  • 00:38 Once you are ready, you can conduct the plan,
  • 00:41 this involves measuring the items and recording the data.
  • 00:44 Based upon the difficulty of the measurement system and
  • 00:46 the ability to gain access to resources, this may take an hour or several weeks.
  • 00:51 The third phase is the analysis, this is very different depending upon whether
  • 00:55 the data was variable data or attribute data.
  • 00:58 The calculations are complex enough, that we'll devote an entire
  • 01:01 lessons to each of these but for now, let's dig a bit deeper into each phase.
  • 01:06 Let's start with the creation of the Gage R&R study plan.
  • 01:09 The first step is rather obvious.
  • 01:11 Decide what measurement you're interested in.
  • 01:14 We need to understand if it is a variable or attribute measurement.
  • 01:17 While this step seems obvious,
  • 01:18 it's not a trivial question on a Lean Six Sigma project.
  • 01:22 It's easy to do a study on what is convenient to measure but
  • 01:25 you need to ask what is important to measure and how will we measure that.
  • 01:30 The next step is an obvious follow from the previous step.
  • 01:33 Now that we know what we're measuring, the question becomes how it is measured.
  • 01:37 What is the current measurement system in process?
  • 01:40 Where is the measurement done?
  • 01:42 What equipment or procedures are used?
  • 01:44 Who does the measurement?
  • 01:45 If there's no existing measurement process, you'll need to create one and
  • 01:49 then your Gage R&R study becomes part of the validation process for
  • 01:52 that measurement system.
  • 01:54 These first two steps will focus our efforts.
  • 01:57 Step 3 is to design the study.
  • 01:59 That means deciding how many appraisers, items and trials.
  • 02:03 There are some differences in the approach, depending upon,
  • 02:05 whether it's variable measurements or an attribute measurement.
  • 02:08 With variable studies, use 5 to 10 items.
  • 02:11 With attribute studies, use 20 to 30 items.
  • 02:15 The easiest way to see the study design is to see the data collection form.
  • 02:20 That's where all of the design parameters are captured.
  • 02:22 I’ll show these forms in the next few slides. Which takes us to step four.
  • 02:27 With the study designed and
  • 02:29 the forms ready, we need to communicate the plan to everyone involved.
  • 02:33 Normally this is quite easy but depending upon what's involved,
  • 02:37 you may need to do things like make special sample items for
  • 02:41 inspection that are known to be out of specification.
  • 02:44 So there may be some cost and time needed to create those items.
  • 02:48 The coordination step is often combined with the previous step.
  • 02:51 It is a coordination of the resources such as facilities equipment, parts for
  • 02:55 inspection and the people needed to run the study.
  • 02:58 When communicating the plan you may wanna start this coordination.
  • 03:02 For instance, you may need to get access to the measurement equipment that
  • 03:05 is being used as part of day to day business operations.
  • 03:08 You'll need to coordinate them with the area supervisor.
  • 03:11 Also, the operators who will be the appraisers need to be identified, so
  • 03:14 that they're relieved from normal duties and available when you run the study.
  • 03:19 Depending upon the complexity of the measurement system,
  • 03:22 you may need support from other organizations.
  • 03:24 This is especially true if you have to conduct the study outside of normal
  • 03:27 business operations such as on a weekend.
  • 03:30 Finally, you need to train the operators in the purpose and process of the study.
  • 03:35 The individuals will need to understand that the study is not a performance
  • 03:39 appraisal on them, it is an evaluation of the system.
  • 03:43 Sometimes they get nervous about the study and
  • 03:45 that creates special cause variation problems in the results.
  • 03:49 Of course, if this is a brand new measurement system or
  • 03:51 process, the appraisers will need to be trained on how to use the equipment.
  • 03:56 Lets now look at the data collection form for variable data, Gage R&R study.
  • 04:01 If using Minitab, a statistical software application commonly used
  • 04:05 with Lean Six Sigma projects, this is easy.
  • 04:08 You just enter your study parameters into the mini tab assistant setup form and
  • 04:12 it generates a study plan complete with the data collection form.
  • 04:16 I'll show you how to do this in a later lesson where I also show you how to use
  • 04:20 Minitab to analyze the data.
  • 04:23 The measurement results from each measurement are then entered right
  • 04:25 into the Minitab form and you're ready for the analysis.
  • 04:29 But if you don't have Minitab,
  • 04:30 don't worry, you can do everything in the spreadsheet such as Excel.
  • 04:34 You will need to create your own data collection form and
  • 04:37 you'll need to put in the equations for your analysis.
  • 04:40 Again, I'll show you how to do those on the variable data Gage R&R lessons.
  • 04:44 As you can in this form, for this study we'll have three appraisers
  • 04:48 who each will measure 10 items and do these three times.
  • 04:52 One of the things that I have also put on this form is that we'll need to calculate
  • 04:55 the averages or means for each appraiser and each part.
  • 04:58 We'll use those in the calculations.
  • 05:00 One caution when planning the study.
  • 05:03 You need to do the measurements in a random order but
  • 05:06 you need to record the data for the correct item.
  • 05:08 So to prevent the appraiser knowing which item they're measuring and
  • 05:11 their previous measurement value,
  • 05:13 I always have someone else record the data who knows which item is which.
  • 05:18 Well, that was for variable data studies.
  • 05:20 The attribute data Gage R&R data collection looks a little bit different.
  • 05:25 The Minitab approach is the same. Enter your study parameters and
  • 05:28 Minitab will create the plan and the data collection form.
  • 05:31 And I'll show you how to do that in the attribute data Gage R&R lesson.
  • 05:36 And like with the variable data, we can do this analysis in a spreadsheet,
  • 05:40 we just need to manually create the form and enter the equations.
  • 05:44 As you can see, the form is different for attribute data.
  • 05:47 We don't have numerical measurements.
  • 05:49 Instead, we have pass-fail or good-bad ratings for each item.
  • 05:53 Once again, I have three appraisers.
  • 05:56 And this time, just two trials are repetitions.
  • 05:59 But with the attribute data, you need more data points.
  • 06:02 So my spreadsheet goes all the way down to data item number 30.
  • 06:07 There are also columns for matches and match to the standard.
  • 06:10 I will discuss those in the lesson on the Attribute Data Gage R&R calculation.
  • 06:16 One of the things about Attribute Data Gage R&R analysis,
  • 06:19 is that it can include an assessment of the effectiveness of the measure,
  • 06:23 in addition to repeatability an reproducibility.
  • 06:26 To do that, we need to know the true value of each item.
  • 06:29 So, we have a column for
  • 06:30 the actual condition of the item labeled standard that's either good or bad.
  • 06:35 Once again, the items need to be randomized in the order of inspection.
  • 06:39 But the correct value needs to be entered for each item.
  • 06:42 So I have someone else recording the data.
  • 06:46 The methodology for planning and executing a Gage R&R study is not difficult.
  • 06:49 The key will be the creation of the data collection form which
  • 06:54 captures the planning and sets us up for the data analysis.

Lesson notes are only available for subscribers.

Gage R&R Principles
06m:00s
Gage R&R Study Design Considerations
07m:08s

PMI, PMP, CAPM and PMBOK are registered marks of the Project Management Institute, Inc.

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