MetricS 125
(B) can you explain defect age and defect spoilage?
Defect age is also called a phase age or phage. One of the most important things
to remember in testing is that the later we find a defect the more it costs to fix
it. Defect age and defect spoilage metrics work with the same fundamental,
i.e., how late you found the defect. So the first thing we need to define is what
is the scale of the defect age according to phases. For instance, the following
table defines the scale according to phases. So, for instance, requirement
defects, if found in the design phase, have a scale of 1, and the same defect,
if propagated until the production phase, goes up to a scale of 4.
Figure 122 Measure test effectiveness
Figure 123 Scale of defect age
126 Software teSting interview QueStionS
Once the scale is decided now we can find the defect spoilage. Defect
spoilage is defects from the previous phase multiplied by the scale. For
instance, in the following figure we have found 8 defects in the design phase
from which 4 defects are propagated from the requirement phase. So we
multiply the 4 defects with the scale defined in the previous table, so we get
the value of 4. In the same fashion we calculate for all the phases. The following
is the spoilage formula. It’s the ratio of the sum of defects passed from the
previous phase multiplied by the discovered phase then finally divided by the
total number of defects. For instance, the first row shows that total defects are
27 and the sum of passed on defects multiplied by their factor is 8 (4 3 1 5
4 1 2 3 2 5 4). In this way we calculate for all phases and finally the total.
The optimal value is 1. A lower value of spoilage indicates a more effective
defect discovery process.
Figure124 Defect spoilage
Figure 125 Spoilage formula
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