INTRODUCTION TO SOFTWARE DESIGN FOR SIX SIGMA (DFSS) - Software Design for Six-Sigma: A Roadmap for Excellence - page 186

problems that are of greatest importance or those causes that seem to account for most
of the variation. Thus, a Pareto chart helps teams to focus their efforts where they can
have the greatest potential impact. Pareto charts help teams focus on the small number
of really important problems or their causes. They are useful for establishing priorities
by showing which are the most critical CTQs to be tackled or causes to be addressed.
Comparing Pareto charts of a given situation over time also can determine whether
an implemented solution reduced the relative frequency or cost of that problem
or cause.
A CTQ tree is used to decompose broad customer requirements into more easily
quantified requirements. CTQ trees often are used in the Six Sigma DMAIC method-
ology. CTQs are derived from customer needs. Customer delight may be an add-on
while deriving CTQ parameters. For cost considerations, one may remain focused
an customer needs at the initial stage. CTQs are the key measurable characteristics
of a product or process whose performance standards or specification limits must be
met in order to satisfy the customer. They align improvement or design efforts with
customer requirements. CTQs represent the product or service characteristics that are
defined by the customer (internal or external). They may include the upper and lower
specification limits or any other factors related to the product or service. A CTQ
usually must be interpreted from a qualitative customer statement to an actionable,
quantitative business specification.
Pugh concept selection is a method, an iterative evaluation, that tests the complete-
ness and understanding of requirements and quickly identifies the strongest software
concept. The method is most effective if each member of the DFSS team performs
it independently. The results of the comparison usually will lead to repetition of the
method, with iteration continued until the team reaches a consensus. Pugh concept
selection refers to a matrix that helps determine which potential conceptual solutions
are best . 15 It is to be done after you capture VOC and before design, which means
after product-planning QFD. It is a scoring matrix used for concept selection, in
which options are assigned scores relative to criteria. The selection is made based on
the consolidated scores. Before you start your detailed design, you must have many
options so that you can choose the best from among them.
The Pugh matrix is a tool used to facilitate a disciplined, team-based process
for concept generation and selection. Several concepts are evaluated according to
their strengths and weaknesses against a reference concept called the datum (base
concept). The Pugh matrix allows the DFSS team to compare differ concepts, cre-
ate strong alternative concepts from weaker concepts, and arrive at a conceptu-
ally best (optimum) concept that may be a hybrid or variant of the best of other
concepts
The Pugh matrix encourages comparison of several different concepts against a
base concept, creating stronger concepts and eliminating weaker ones until an optimal
concept finally is reached. Also, the Pugh matrix is useful because it does not require
a great amount of quantitative data on the design concepts, which generally is not
available at this point in the process.
15 El-Haik formulated the Concept Selection Problem as an integer program in El-Haik (2005).