Repeating a refuted item doesn’t make it true

mistakeWith the election just over,  I am reminded that politicians will repeat things that have been refuted. What reminded me was an article in Clinical Laboratory News about risk management. Here is such a quote from the article:

“According to Yost, many labs have implemented EQC successfully with no other quality problems identified during inspections. She also commented that with unit-use devices, doing QC on one cartridge doesn’t really tell you much about the performance of the rest of the cartridges, anyway. “You’re just using up a cartridge, whereas internal  controls can tell you a whole lot more about the test system,” she said.”


This quote actually has two problems. I have commented before that because no problems have been identified during inspections does not justify that EQC is a good thing to do. I said that if you take the airbags out of a car, and there are no crashes, the safety results of the car will be fine. This does not justify the removal of airbags.


But I am more interested in the second problem which implies that QC is useless for unit use devices, because a unit use device is used up during the test. This is also in the latest draft of EP23, which I won’t quote, since it is a draft.


The problem is this statement implies that all problems are random occurrences. This is simply not true. When problems are random by the way, the same problem with QC applies to non unit use devices. That is, the failed sample does not inform about other samples.


But many problems are not random but occur systematically for each sample until either the problem goes away or is identified and the system is stopped. This is shown in the following figure for both unit use and non unit use devices.




In this figure in the unit use case, the factory is making thousands of unit use devices, but there is a problem (shown in red). All of the unit use devices are bad. Of course, the factory has its own QC procedures to guarantee that bad units are not released but this QC procedure also fails leading to thousands of bad units being shipped.


That QC can fail at the factory is a point that most people have problems with. Well, it happens.


The clinical laboratory performs QC on the system. QC detects this systematic problem and no bad  results are reported until the problem is solved (e.g., another lot of unit use devices is used).


In the non unit use case, a similar situation occurs. A bad reagent is shipped to a clinical laboratory, which detects this by running QC.



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