QA glossary
What is the cost of quality?
The cost of quality is the total a business spends because software can have defects: preventing them, finding them, fixing them before release and dealing with them after release. Splitting the spend into those four categories shows where the money goes and makes the business case for testing.
The four categories
- Prevention costs: planned work that stops defects being made, such as training and reviewing requirements early.
- Appraisal costs: work that finds defects, such as static and dynamic testing and reviews.
- Internal failure costs: fixing defects found before release, and the workarounds.
- External failure costs: everything a defect costs once a customer has it: lost revenue, legal costs, support, and fixing and redeploying in the field.
This is the model in the ISTQB Test Management syllabus (CTAL-TM v3.0, section 3.2.1), based on Feigenbaum's approach. The syllabus notes that appraisal and internal failure costs together are usually far smaller than external failure costs, which is what makes testing worth paying for.
An example from QA practice
A product team adds up one quarter. Code reviews and a short training session are prevention. The test team's time is appraisal. Developer hours spent fixing bugs found in testing are internal failure. A pricing bug that reached customers brought refunds, support tickets and an emergency release: external failure. The last category is the largest, and it is the one the team can shrink by moving spend into the first two.
How BetterQA does it
Testing is an appraisal cost, and our job is to move spend out of the external failure column. Every defect we log in BugBoard records where it was found, so a client can see how many were caught before release and how many escaped, the same data that defect leakage is calculated from. We only test, we never build, so our figures are not marking our own work.
Related terms
The four cost categories, and where a quality budget goes.