One accurate measurement worth a thousand expert opinions
Grace Murray Hopper
“A statistical analysis of a measurement system to determine variability of the measurement system”
In Laboratory all the drug product and drug substance are tested by laboratory analyst by using different instruments and definitely there would be little variation among the analyst as well measuring devices,sometime known as tolerances. Measurement system analysis is a tool to identify and validate analyst and instruments variations. it should be only common cause variable.
Two kind of measurement system is performed based on category of data. For discrete(Pass/Fail, Yes/No) data Attribute agreement analysis is performed.For continuous data(weight, scale,infinite numbers) Gauge R&R tool can give desired result.
In measurement system analysis we need to evaluate the variability between analyst and instrument which are commonly known as Gauge R&R(Repeatability & Reproducibility).Gauge is used for measuring variability in measuring instrument and covers three basic model of Bias.i.e Accuracy,Linearity and Stability.one more important aspect is sensitivity, whether the gauge is sensitive enough to detect differences measurement as slight as one tenth of total tolerance specification or process spread.Another part in measurement system is Precision which talks about variations within the appraiser/analyst/operator.sometimes also known as Repeatability and Reproducibility.
Every measurement system consist of following key components:
- Measurement instrument/device
- Appraisers/Operator
- Method for conducting measurement
- Environment
To conduct Gauge R&R we must ensure that instruments are calibrated with national standards(reference standard)
Two well known methods are available in Gauge R&R
- Control Chart Method(Xbar R Chart)
- ANNOVA Method
Control Chart Method: In this 5 different variation are measured.
Gage R&R-Short Method is a tool used to assess the variation in a measurement system due to the combined effect of reproducibility and repeatability. An advantage of this tool is that it requires only two operators and five samples to complete the analysis. A disadvantage of this tool is that the individual effects of repeatability and reproducibility cannot be separated. This tool applies to continuous data only
- Equipment Variation(EV): estimate of the standard deviation of the variation due to repeatability(EV/TV*100)
- Appraiser Variation(AV): an estimate of standard deviation of the variation due to reproducibility(AV/TV*100)
- Gauge R&R : an estimate of standard deviation of the variation due to measurement system(GRR/TV*100)
- part to part variation(PV): an estimate of standard deviation of the variation due to part differences(PV/TV*100)
- Total Variation(TV): estimate of standard deviation of the total variation in the study.square root of GRR^2 and PV^2
Users can use below link to get Excel template for capturing appraiser data.
https://www.moresteam.com/university/downloads/VariablegaugeRandR.xls
Decision for the GRR can be done on below criteria:
ANNOVA method shall be covered in next blog………….
All about Pharmaceuticals & Medical Devices 