Information Technology Reference
In-Depth Information
Quality cost is the cost associated with preventing, finding, and correcting defective
work. The biggest chunk of quality cost is the cost of poor quality (COPQ), a Six
Sigma terminology. COPQ consists of those costs that are generated as a result of
producing defective software. This cost includes the cost involved in fulfilling the
gap between the desired and the actual software quality. It also includes the cost of
lost opportunity resulting from the loss of resources used in rectifying the defect.
This cost includes all the labor cost, recoding cost, testing costs, and so on. that have
been added to the unit up to the point of rejection. COPQ does not include detection
and prevention cost.
Quality costs are huge, running at 20% to 40% of sales (Juran & Gryna, 1988).
Many of these costs can be reduced significantly or avoided completely. One key
function of a Quality Engineer is the reduction of the total cost of quality associated
with a product. Software quality cost equals the sum of the prevention costs and the
COPQ as defined below (Pressman, 1997):
1. Prevention costs: The costs of activities that specifically are designed to prevent
poor quality. Examples of “poor quality” include coding errors, design errors,
mistakes in the user manuals, as well as badly documented or unmaintainable
complex code. Note that most of the prevention costs does not fit within the
testing budget, and the programming, design, and marketing staffs spend this
money. Prevention costs include the following:
a. DFSS team cost
b. Quality planning
c. Formal technical reviews
d. Test equipment
e. Training
2. Appraisal costs (COPQ element): The are costs of activities that are designed to
find quality problems, such as code inspections and any type of testing. Design
reviews are part prevention and part appraisal to the degree that one is looking
for errors in the proposed software design itself while doing the review and
an appraisal. The prevention is possible to the degree that one is looking for
ways to strengthen the design. Appraisal cost are activities to gain insight into
product condition. Examples include:
a. In-process and interprocess inspection
b. Equipment calibration and maintenance
c. Testing
3. Failure costs (COPQ elements): These costs result from poor quality, such as
the cost of fixing bugs and the cost of dealing with customer complaints. Failure
costs disappear if no defects appeared before shipping the software product to
customers. It includes two types:
a. Internal failure costs—the cost of detecting errors before shipping the prod-
uct, which includes the following:
i. Rework
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