The formal version of “Six Sigma can be dangerous to our health”

August 31, 2008

I have previously blogged about this topic, here. Now, a more formal version has been published, first as an online version, here. Due to copyright rules, I cannot post this version (for a year). It is a cleaned up and somewhat expanded version of the blog version.

The point of this paper is not so much to criticize Six Sigma, but more on how it is used (or misused). That is, certain proponents of six sigma use it as a sole measure of quality – which in clinical laboratory terms, means a sole measure of potential patient harm. One is reminded of the manufacturer customer dilemma. Thus, a manufacturer, must either accept or reject product, often based on a single limit whereby accepted product is equated  with full value and rejected product is scrap. But to a customer, product which is just meeting or just not meeting specification is similar in value – hence the manufacturer’s model, while necessary, doesn’t transfer well to the customer. The manufacturer has a dichotomous model and the customer has a quadratic model.

Now manufacturers can’t use a quadratic worth model to make decisions – it’s impractical, but they can do better than a single acceptance limit. Hence, having two sets of acceptance limits, one to contain a high proportion (such as 95%) of results and the other to contain few or no results – helps to have a more customer oriented specification and correct specifications are an ideal starting point for most projects.

I had proposed using a process capability metric (Cpm) to evaluate laboratory assays (1) but here, I had also proposed that in addition to calculating Cpm, one must estimate the proportion of values that fall outside of medically acceptable limits.


1. Assay Development and Evaluation: A Manufacturer’s Perspective. Jan S. Krouwer, AACC Press, Washington DC, 2002, pp 96-101.

So many blogs

August 15, 2008

I’ve finally added a blog roll – links to other blogs. Actually, I have many more blogs saved under feeds, but I find that many of these feeds I don’t read thoroughly – more like a quick scan. The blogs listed here, however, I do read. In the field of healthcare, I have only one blog listed – The Covert Rationing Blog. I recommend it highly. At the end are two windsurfing blogs. The picture on the left is my view (literally) on windsurfing – from a helmet cam. For a longer version, go here or here.

CLSI EP22 EP23 Review

August 4, 2008

EP22 was created as a means to use risk management to allow manufacturers to recommend the frequency of external quality control run by clinical laboratories. This was the so called option 4. Options 1-3 were part of the original CMS proposal to allow clinical laboratories to reduce the frequency of external quality control to once a month (provided certain conditions were met).




EP23 was the clinical laboratory follow on document to EP22.

Here’s my take on these two documents.

1.       Manufacturers won’t provide the information as suggested by EP22. (This information consists of experiments to demonstrate the efficacy of internal control measures). It would be a lot of work (e.g., cost) and there’s no regulatory requirement to do so. Moreover, if this information were provided, then it is labeling which would require FDA to review it. It is not clear that FDA has accepted this review task. 

Update on 8/4/08 – During a CLSI presentation at the AACC meeting in Washington, Alberto Gutierrez from the FDA gave a presentation. Afterwards, I asked him if FDA would review the material about internal control experiments that manufacturers might present as part of the package insert. He said that FDA would review this material – but from what was said it seemed that the review would be superficial and that only egregious problems would be flagged by the FDA.

2.       Clinical laboratory staff does not have the expertise to review this information, were it provided. This does not mean that clinical laboratory staff is incapable of reviewing it – they could acquire the expertise – it just seems unlikely.


3.       Should manufacturers provide this information and clinical laboratory staff review it, there would be no benefit with respect to improving QC. This is illustrated by an example in EP22 where the failure mode of “incorrect results due to low volume sample” is examined. After presenting the results of an experiment to show how an internal system control works, the user control measure is to “ensure that adequate volume of sample is presented to instrument.” But clinical laboratory staff would (or should) do this anyway. They don’t need EP22 and EP23 to know that one should follow the manufacturer’s instructions and to refrain from doing something stupid.


In clinical chemistry, risk management is “in.” But there are signs that its popularity is already starting to wane. This is unfortunate, as there is a great opportunity to use risk management tools to reduce both the risk and occurrence of laboratory errors. But one must focus not just on potential system errors, as EP22 and EP23 do, but on human errors as well.