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An OPSpecs Chart shows the operational limits for bias and imprecision for the specified candidate QC procedure at either 90%, 50%, or 25% analytical quality assurance (AQA or error detection).
TEa
Total allowable error. The quality requirement for the test.
In the example above, the TEa is 25%.
AQA (SE)
Analytical quality assurance for systematic error. The percentage of error detection. In the example above, the AQA is 90%.
Allowable Imprecision (x-axis)
The allowable imprecision (bias) scaled from 0 to 0.5 TEa.
Allowable Inaccuracy (y-axis)
The allowable inaccuracy (bias) scaled from 0 to TEa.
Maximum limits of a stable process
The highest line on the chart describes the maximum limits of inaccuracy and imprecision for a method that is perfectly stable and does not need any quality control.
Limits of bias and imprecision for suggested QC procedure (Operating Limits line)
The lowest line on the chart describes the limits of bias and imprecision for the suggested QC procedure with the selected quality control procedure. The line is labeled with the suggested QC rules (1-3s in the example). The Operating Point should be below this line.
Operating Point
The Operating Point shows where the test's bias and imprecision intersect and shows the observed performance of the measurement procedure. The Operating Point is plotted by obtaining estimates for imprecision and inaccuracy and using them as X (imprecision) and Y (inaccuracy) coordinates on the chart.
Operational limits depend on the guarantee of quality built into the process. For example, operational limits for 90% AQA are more demanding than those for 50% AQA. Lower assurance, or lower error detection, may be acceptable for very stable testing processes with a very low frequency of errors. However, in general it is best to aim for 90% AQA.
If any of the lines in the OPSpecs Chart are above the Operating Point, they meet or exceed the level of quality assurance listed in the chart's title. For example, if the Operating Limits line is above the Operating Point in a 90% AQA Chart, the control rule and N (the recommended number of control determinations) corresponding to that line assures 90% or more analytical quality assurance or error detection.
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