Page 135 - Design for Six Sigma for Service (Six SIGMA Operational Methods)

110 Chapter Six

The correlation matrix is one of the more commonly used optional extensions
to the original QFD developed by Kobe engineers. Traditionally, the major
task of the correlation matrix is to make tradeoff decisions by identifying the
qualitative correlations between the various Hows. This is a very important
function in the QFD because Hows are most often correlated. For example,
assume a matrix contains quality and cost objectives. The design engineer is
looking to decrease cost, but any improvement in this aspect will have a
negative effect on the quality. This is called a negative correlation, and it
must be identified so that a tradeoff can be addressed. Tradeoffs are usually
accomplished by revising the long-term objectives (How Muchs). These
revisions are called realistic objectives. Using the negative correlation
example just discussed, in order to resolve the conflict between cost and
quality, the cost objective would be changed to a realistic objective.

In the correlation matrix, once again, symbols are used for ease of reference
to indicate the different levels of correlation as shown in the following figure:

Trade offs
Synergy + 1.0
Compromise − −1.0

If one How directly supports another How, a positive correlation is
produced.

Targets (How Much)
For every How shown on the relationship matrix, a How Much should be
determined. The goal here is to quantify the customers’ needs and expec-
tations and create a target for the design team. The How Muchs also create
a basis for assessing success. For this reason, Hows should be measurable.
It is necessary to review the Hows and develop a means of quantification.
Target orientation to provide a visual indication of the target type is usually
optional. In addition, the tolerance around targets needs to be identified,
based on the company marketing strategy and contrasting it with the best-
in-its-class competitor. This tolerance will be cascaded down using the
axiomatic design method.

Competitive Assessments or Benchmarking
Competitive assessments are used to compare the competition’s design with
the team design. There are two types of competitive assessments:
1. Customer competitive assessment: Found to the right of the rela-
tionships matrix in the planning matrix. Voice of the customer (VOC)