Smith’s Taxonomy of Quality Problems

If you’re going to select a strategy for process improvement, sometimes it’s good to know what category your problem falls in. Then, you can choose solutions for other problems in the same category that were solved! That’s the subject of Smith’s article in Quality Progress in 2000.

In practice, Smith says, there is often a need to “fit problem solving responses to the nature of the situation.” (Smith, 2000) To do this, the solution space describing possible characteristics of situations must be identified. His taxonomy, derived from an empirical review of 719 cases from 242 sources in the literature, is one attempt to characterize the realm of possibilities that arise when you embark on a process improvement effort.

Smith found that there was a consistent distinction between performance problems and design problems. He also noted that this was consistent with an earlier taxonomy proposed by Nickols, which classified all quality problems as repairs, improvements, or engineering activities. The consistency derives from the fact that performance improvement may be achieved not only by repairing and improving an existing system, but potentially also by reengineering it. The lowest level of Smith’s taxonomy reveals five classes of quality problems that are encountered in practice: conformance problems, unstructured performance problems, and efficiency problems (which are all related to performance), and design problems, subdivided into product design and process design problems.

But what goals are you trying to accomplish when you are solving quality problems? When expressed in terms of the goals evident in Okes & Westcott (2003) and the ASQ Body of Knowledge for several specializations, it is evident that the most common goals are all accommodated by the model except alignment with the voice of the customer. Also, the model does not effectively take into consideration that sometimes a problem that requires new design (whether it is process design or product design) requires evaluating and responding to performance problems. For that reason, I think Smith’s model should be adjusted to account for three top level problem categories, each of which is influenced by the connection with the customer and each of which can be analyzed in light of performance problems.

Top level problem categories are all Customer/Environment Alignment Problems (capturing and responding to the voice of the customer):

  • Design-Independent Problems
  • Product Design Problems
  • Process Design Problems

For each of the three problem categories above, performance problems can be classified into one of these three areas:

Conformance Problems

  • Achieve conformity to standards or specifications
  • Prevent defects (improve accuracy/integrity, prevent human error)
  • Reduce variation

Efficiency Problems

  • Eliminate waste/rework (incl. non-value-adding activity)
  • Improve productivity
  • Improve efficiency and effectiveness

Unstructured Performance Problems

Problems with aesthetics, taste/preferences, or perceived quality would be addressed as unstructured performance problems, typically regarding the product design. However, if service quality is the item of interest, we can also consider that these issues involve process design (and the process is just extended to involve customers as the primary stakeholder). Smith’s framework covers many cases of quality problem solving that address objective quality (characteristics that can be measured with universal agreement and for which all customers prefer either a higher or lower magnitude), but does not take into account the impacts of perceived quality. This gap is filled by a study that originated in the marketing discipline (Mitra, 2003) which also provided the definition of objective quality above.

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