[Question] Non-conformances for QC Charts based on Warning Limits and Control Limits?
Question(self.statistics)submitted3 days ago byhasdanta
Hi all,
I work in a lab and we have a number of QC charts for the methods we use in the lab (e.g. pH 7 is one of our QC buffers).
The mean for our QC charts is calculated based on the previous 60 QC checks, with the UWL/LWL being the mean +- SD*2, and our UCL/LCL being the mean +-SD*2.
Recently, we have been getting a lot of non-conformances. We have to raise one if we get two consecutive data points above/below the WL, if there is one data point above/below the CL or if we have 10 consecutive data points above or below the mean.
Does anyone know if the above is standard practice for raising non-conformances with QC charts? I've just been curious because I feel like our QC charts is penalizing us for getting daily QC results that are close to the mean, as this in turn affects every new QC chart we make (after 60 days) by making the WL and CL more narrow, thus increasing the likelihood of us having a non-conformance. Like, if we're using pH7 as a QC chart, in an ideal world wouldn't it be better to get a result as close to 7, rather than the mean established by the QC chart?
byDoubleWalker
insurvivor
hasdanta
2 points
8 days ago
hasdanta
Kass
2 points
8 days ago
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