Whats the best way to chart QC for multirule applications?
You can chart your QC data using regular Levey-Jenning’s control charts, on which additional lines have been drawn to represent the mean plus/minus 1s, plus/minus 2s, and plus/minus 3s. You can set up one control chart for each level of control material being analyzed. These individual charts have the advantage of showing your method performance at each control level. However, it is difficult to visually combine the measurements from consecutive control measurements on different materials. To combine measurements on different materials, you can first calculate the difference of each control observation from its expected mean, divide by the expected standard deviation to give a z-score or a standard deviation index (SDI), and then plot the SDI value on a control chart whose central mean is zero and whose control limits are drawn as plus/minus 1, plus/minus 2, and plus/minus 3. You can plot the values for the different materials using different colors to help keep track of trends within
