Page 123 - The Six Sigma Project Planner

Process Metrics

Six Sigma projects operate upon business processes. These processes are designed to
deliver something of value to a customer, such as a product or a service. For this reason,
these processes are sometimes called customer value streams. The purpose of most Six
Sigma projects is to improve business processes so that they deliver greater value to
customers. In this section you will determine precisely how the success of these efforts
will be measured.

What Are the Key Metrics for This Business Process?
Six Sigma process metrics typically fall into one of three major categories: quality, cost,
or schedule. These characteristics are critical to the success of the enterprise and are
thus commonly referred to as “critical to” characteristics. A critical-to-quality
characteristic (CTQ) is one that impacts on the fitness for use of the product or service
produced by the process. A critical-to-cost (CTC) characteristic has a significant impact
on the cost to produce the product or service. A critical-to-schedule (CTS) characteristic
has a significant impact on the ability to deliver the product or service in a timely
manner. Collectively, these are often called CTx characteristics, where x = Q for quality,
C for cost, and S for schedule.

Note that it is often difficult to separate a metric into one and only one category. For
example, if a Six Sigma project involved a coffee mug manufacturing process, a crack in
a coffee mug would be classified as a CTQ characteristic even though cracked mugs also
impact cost and schedule. Normally, the CTx is assigned to the dominant effect; in this
case it is quality. An example of a CTC characteristic for the coffee mug process might
be the energy consumed firing the ceramic. A CTS characteristic might be the timeliness
of raw material deliveries.

DPMO Definition
Defects-per-million-opportunities (DPMO) criteria must be carefully defined. The defect
must be described in clear, rigorous, and unambiguous terms. Defect definition often
includes photos, physical specimens, or other inspection aids. Similar attention must be
given to the opportunity used as the base. Opportunities are events or characteristics that
might be incorrect.
Example: Wave solder. A defect would be an improperly produced solder joint. The
defect might be missing solder, incomplete solder, poor solder bond, grainy solder,
short circuits, etc. Each of these defects would be carefully defined and personnel
would be thoroughly trained to identify each. A single solder joint might have several
defects; all would be counted. The opportunities would be solder joints. DPMO would
be calculated for this process as follows:
DPMO = 1,000,000 defects (Equation 1)
number of solder joints

For example, for a circuit board with 1,000 solder joints and 5 defects, the DPMO would
be:

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