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Secondary Metric


Secondary Metric in a project is one that has to be kept constant or prevented from deterioration as it is an important process metric even though it is not the metric to be improved. Hence, the objective of the project is twofold
1. Improve the project CTQ or the primary metric
2 Keep the secondary metric constant


Review the answer provided by Mr Venugopal R, Benchmark Six Sigma's in-house expert.


Q. 154  Give some good examples, preferably from different Industries, where a Lean Six Sigma project was considered successful w.r.t Primary Metric (CTQ) but was later understood to be a big failure due to adverse impact on Secondary Metric. 


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Benchmark Six Sigma Expert View by Venugopal R


Let me narrate an incident from a layman perspective.


After buying a large furniture from a well reputed company it had to be assembled after being delivered at home. Since the company mechanic was not turning up at the agreed time, I had to call up and urge him to come fast. When he arrived and started work, I observed him struggling with certain fasteners. Concerned about his capability, I questioned him why he was finding it so difficult. He said he had not brought the special tools required for the job… and he also added that he forgot them, since I asked him to hurry up! So bluntly, the blame was on the customer!


Now, this response led me to think that I had stressed upon the company to get my work done fast (that too since they did not stick to agreed time), so the time for completing the job was the “Primary metric”, but I had not cautioned him to maintain any “Secondary Metric” – viz. “To ensure that necessary tools are not left behind”. His irresponsibility is being justified for me not having specified the ‘secondary metric’! I also wondered how many more secondary metrics should I have specified!


The secondary metric is a factor that we do not want to compromise (knowingly or unknowingly), while we pursue to improve our primary metric (CTQ).


In the above incident the failure by the mechanic and his reply reflects his callous attitude, though in effect, a secondary metric was compromised.


However during business decisions, there could be unanticipated failures that could arise due to failure in a secondary metric, which happen to be a potential “Contradicting Factor” to the primary metric.


Let me explain a couple of experiences where the secondary metric was not identified pro-actively and resulted in failures.


The first one is a case where the sourcing of certain component of an IT hardware product had to be changed for reducing the import costs. The component samples obtained from new source were subjected to all evaluations, validations and pilot tests as per applicable standards and implemented. A few days after implementation, many field failures pertaining to this component started erupting. Upon detailed investigation and root cause analysis, it was revealed that the new component had been subjected to all the tests and validations that used to be done for the old one and approved as fit. However, there were certain special operating conditions under which some of the new components failed. These conditions had never been part of the part approval protocol, though the old component had been unobtrusively withstanding those conditions. This was a secondary metric that should ideally have been considered, but it was never known until the damage was done.


Now, let’s look at another experience from IT services industry, where a particular instruction pertaining to certain data processing was simplified using automation techniques. Here the primary metric was to improve productivity. However, after implementation, it was observed that there were processing failures by experienced processors, whereas the processing quality by new processors was very good. The secondary metric that was missed out in this situation was that the ‘effective unlearning’ by the experienced processors, who continued to apply certain instructions that were no longer necessary.


In both above cases the secondary metrics that turned out to cause failures were missed out while chartering the project. It is recommended that a fresh FMEA be carried out while implementing such changes so that as many potential failure modes may be surfaced and the associated secondary metrics addressed pro-actively.

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It is necessary to have secondary metrics when we drive Six Sigma projects so that we are not solving one problem and creating another. In other words, we wouldn't be solving problems but they would just be changing shape. There could be several examples where the project fails despite improvement in the primary metric. Let's see a few here -


1. Customer Satisfaction increases but handling time increases

2. Order to ship time decreases but wrong deliveries increase

3. Order processing time of a certain component decreases but field failures increase

4. First Call Resolution increases but Handle Time also increases

5. A hair color that starts lasting longer but more users report damaged hair

6. Oil paints that dry faster but the pigments fade away faster.


Please read the expert view given by Venugopal.

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