Defect age is also called as Phase Age or Phage. One of the most important things to remember in testing is later we find a defect more it costs to fix. Defect age and Defects spoilage metrics works on 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 below table defines the scale according to the Phases. So for instance requirement defects if found in design phase has a scale of 1 and the same defect if propagated till the production phase goes up to a scale of 4.
Figure: - Scale of Defect Age
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 below 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. Below given is the spoilage formula. It’s the ratio of 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 sum of passed on defects multiplied by their factor is 8 ( 4 x 1 = 4 + 2 x 2 = 4). In this way we calculate for all phases and finally the total. The optimal value is 1. Lower value of spoilage indicates more effective defect discovery process.
Figure: - Defect Spoilage
Figure: - Spoilage formulae