Issues to Consider
- Statistical out-of-control events.
- Frequency of outliers (QC values outside the established total allowable error limits) during the period or across periods.
- The amount of bias present, if any.
Assessing these issues is key to a productive review and can be facilitated by asking the following questions:
- Are the statistical process control (SPC) rules in effect for the test too restrictive when the capability of the methodology or technology and TEa are considered jointly?
- Should another more stringent single rule or more complex multi-rule be applied to improve error detection?
- Should the mean for the test be adjusted?
- How much imprecision is present and is it a significant contributor to total error? Should the laboratory focus its efforts on improving precision?
- How much comparative bias is present and is it a significant contributor to total error? Should efforts be focused on removing or reducing analytical bias?
- Is the appropriate consensus group (Peer, Method, All Labs) being used to estimate the laboratory's comparative bias for the test?
- Are the performance goals for test imprecision and bias (which also affect TEa), set appropriately?
- How frequently do SPC errors occur for the test during the review period? Are the errors across review periods? Are frequent errors due to inappropriate selection of SPC rules, larger than expected imprecision, or the presence of bias? Does the mean and range need adjustment?
- How frequently is the test being recalibrated? Does calibration exceed the frequency recommended by the manufacturer?
There is probably not enough time to ask all of these questions during each review cycle. However, each of these questions represents an opportunity to measure and appraise the effectiveness of the process control in effect for a specific test.
