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Control Charts A Benchmark of Quality

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Page 1: Control Charts - cdnmedia.eurofins.com

Control Charts A Benchmark of Quality

Page 2: Control Charts - cdnmedia.eurofins.com

What is a Control Chart?

A statistical tool used in quality control to:

o Analyze and understand variability for a particular method

o Determine a method’s consistency and capability

o Monitor effects of the variability for a method on the difference between

target and actual performance.

o Limits may be adjusted to allow for more or less variability.

Page 3: Control Charts - cdnmedia.eurofins.com

Anatomy of a Control Chart:o Y-Axis: The unit of measurement for the process (i.e. %, ppm, etc.)

o X-Axis: The date; usually spanning days, months, or years

o Black center line: The average of the process’ compiled data

o Thin black line: ± 1 standard deviations from the average

o Blue dotted line: ± 2 standard deviations from the average

o Red line: ± 3 standard deviations from the average

o The red line represents the upper and lower control limits (UCL and LCL)

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13.00Average:

Variable2Variable3Variable4Variable5Variable6Variable7Variable8+1Stdev:

-1StDev:

+2StDev:-2StDev:

+3StDev:

Page 4: Control Charts - cdnmedia.eurofins.com

Assessing the Data

o Data will naturally have variation based on many variables (i.e. human error,

control degradation, accuracy of method)

o Want data to stay within ± 2 standard deviations of average

o Do not want data to go outside of ± 3 standard deviations or it will be

outside the upper or lower control limits (Red Line)

o After 20 tests have been completed, the limits may be set for a chart by

Quality or relevant personnel

o Control charts should be reviewed by analysts daily upon entering data and

by Technical Managers and QUA at minimum every two months

Page 5: Control Charts - cdnmedia.eurofins.com

Assessing the Data (Part 2)o Certain patterns of data require special attention if found:

o Trends: 6 or more consecutive points increasing or decreasing

o Biases: 8 or more consecutive points on the same side of the center line

o Oscillatory Trend: 14 or more points oscillating back and forth

o These situations do not pose an immediate problem, but should be

monitored. If the process does not correct itself:

o Notify supervisor

o Initiate OOS investigation to determine the cause

o Hold or recall data depending on findings of OOS investigation

o Document OOS investigation and any preventive action

o Requires the interaction of the Technical Manager, QUA, laboratory

management and other relevant personnel

Page 6: Control Charts - cdnmedia.eurofins.com

Duplicate Control Charts

o Two preparations of one sample using the same method with identical

conditions by the same analyst using the same equipment within a short

time interval (same day)

o Provides a measure of method precision/repeatability

o Monitor the difference in the analyzed value of the duplicate by plotting

the results.

o Ensure analysis meets method requirements.

o Duplicates serve as a way for a lab to demonstrate reproducibility by our

analysts for our methods.

Page 7: Control Charts - cdnmedia.eurofins.com
Page 8: Control Charts - cdnmedia.eurofins.com

Relative Standard Deviation

o An RSD (%) shows the analytical variance of a particular test method,

regardless of the sample

o The RSD is already calculated in the control charts and changes as more

data is entered automatically

o Depending on the method, higher or lower RSD’s are accepted for control

charts. (i.e. Enzymes are allowed more variability because enzymatic

activity is not always consistent)

o For most methods, an RSD of >10% is a red flag. It shows too much

variability for that method

o To calculate an RSD:

o RSD% = (Standard Deviation/Average)*100

Page 9: Control Charts - cdnmedia.eurofins.com

Measurement of Uncertainty

Page 10: Control Charts - cdnmedia.eurofins.com

Thank You!