Control Charts A Benchmark of Quality 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. 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) 13.00 Average: 12.00 Variable 11.00 2 Variable 3 10.00 Variable 4 Variable 9.00 5 Variable 6 8.00 Variable 7 Variable 8 7.00 +1Stdev: 6.00 -1StDev: +2StDev : 5.00 -2StDev: +3StDev : 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 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 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. 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 Measurement of Uncertainty Thank You!.