Pros and cons of Six Sigma: an academic perspective

by Jiju Antony on 7th January 2008

The challenge of having quality data available, especially in processes where no data is available to begin with (sometimes this task could take the largest proportion of the project time).
In some cases, there is frustration as the solutions driven by the data are expensive and only a small part of the solution is implemented at the end.
The right selection and prioritisation of projects is one of the critical success factors of a Six Sigma program. The prioritisation of projects in many organisations is still based on pure subjective judgement. Very few powerful tools are available for prioritising projects and this should be major thrust for research in the future.
The statistical definition of Six Sigma is 3.4 defects or failures per million opportunities. In service processes, a defect may be defined as anything which does not meet customer needs or expectations. It would be illogical to assume that all defects are equally good when we calculate the sigma capability level of a process. For instance, a defect in a hospital could be a wrong admission procedure, lack of training required by a staff member, misbehaviour of staff members, unwillingness to help patients when they have specific queries, etc.
The calculation of defect rates or error rates is based on the assumption of normality. The calculation of defect rates for non-normal situations is not yet properly addressed in the current literature of Six Sigma.
Due to dynamic market demands, the critical-to-quality characteristics (CTQs) of today would not necessarily be meaningful tomorrow. All CTQs should be critically examined at all times and refined as necessary (Goh, 2002).
Very little research has been done on the optimisation of multiple CTQs in Six Sigma projects.
Assumption of 1.5 sigma shift for all service processes does not make much sense. This particular issue should be the major thrust for future research, as a small shift in sigma could lead to erroneous defect calculations.
Non-standardisation procedures in the certification process of black belts and green belts are another limitation. This means not all black belts or green belts are equally capable.
Research has shown that the skills and expertise developed by black belts are inconsistent across companies and are dependent to a great extent on the certifying body. For more information on this aspect, readers are advised to refer to Hoerl (2001). Black belts believe they know all the practical aspects of advanced quality improvement methods such as design of experiments, robust design, response surface methodology, statistical process control and reliability, when in fact they have barely scratched the surface.
The start-up cost for institutionalising Six Sigma into a corporate culture can be a significant investment. This particular feature would discourage many small and medium size enterprises from the introduction, development and implementation of Six Sigma strategy.
Six Sigma can easily digress into a bureaucratic exercise if the focus is on such things as the number of trained black belts and green belts, number of projects completed, etc. instead of bottom-line savings.
There is an overselling of Six Sigma by too many consulting firms. Many of them claim expertise in Six Sigma when they barely understand the tools and techniques and the Six Sigma roadmap.
The relationship between cost of poor quality (COPQ) and process sigma quality level requires more justification.
The linkage between Six Sigma and organisational culture and learning is not addressed properly in the existing literature.
The “five sigma” wall proposed in Mikel Harry’s book, Six Sigma: The Breakthrough Management Strategy Revolutionising the World’s Top Corporations, is questionable. Companies might redesign their processes well before even four sigma quality level. Moreover, it is illogical to assume that the “five sigma” wall approach is valid for all processes (manufacturing, service or transactional). Moreover, the decision of re-design efforts over continuous improvement depends on a number of other variables such as risk, technology, cost, customer demands, time, complexity, etc.

What does the future hold for Six Sigma?

In my opinion, Six Sigma will be around as long as the projects yield measurable or quantifiable bottom-line results in monetary or financial terms. When Six Sigma projects stop yielding bottom-line results, it might disappear.