To balance the quality of a product and the time spent looking for failures, we need some measurement to estimate how well we are doing.

COQ takes into account the following costs:

**Failure costs**: All costs of fixing a defect e.g. Patching a deployed product, using the debugger, reviewing code, etc**Appraisal costs**: Work done evaluating whether a product has defects, excluding time spend on fixing them.**Prevention costs**: Resources used to improve the process to reduce the number of defects.

Following I will describe the PSP approximation to COQ a simplified way of calculating this measurement. The author states than this version of COQ shows the same effectiveness as the long COQ version.

- Failure costs: all compiling time, all testing time.
- Appraisal cost: All review time

Cost of Quality is calculated as a percentage of total development time:

**Appraisal COQ**: Sum of all review time as percentage of total development time.**Failure COQ**: Sum of all compile and test time as percentage of total development time.