Process Area 5.1 – Defect Prevention – SG 1 – Determine Common Causes of Defects

Root and common causes of selected defects are systematically defined.

Specific Practices

SP 1.1 Define defect selection parameters and defect classification scheme

SP 1.2 Select defects for analysis

SP 1.3 Analyse causes of selected defects

The purpose of this Goal is to ensure that not only are defects found, but there is an attempt made to reduce the introduction of them as early as possible.

This is done by going back to the root cause of where the defect originated .

It will not usually be possible for an organisation to be able to carry out root cause analysis on every defect raised. It is thus necessary to have some selection criteria by which the full set of defects can be reduced to just those that are most important to the organisation. Maybe just severity 1 defects are selected, or just those that made their way into live. Maybe just those that have the greatest impact on users or those that cost the organisation most money would be selected.

The defect classification scheme that has already been defined in the incident management process can be used, expanded if necessary.

There are many techniques that can be used in root cause analysis including:

  • The 5 (or 7) whys
  • Fishbone (Ishikawa) diagrams
  • Cause-effect diagrams
  • Flowcharting
  • Affinity diagrams
  • Fault tree analysis
  • Kepner-Tregoe Technique
  • Failure mode and Effects Analysis (FMEA)
  • Rapid problem resolution (RPR) diagnosis
  • Check-lists
  • Use of standard defect classifications (e.g. IEEE1044)
  • Process analysis
  • Hardware / software interaction analysis
  • Brainstorming (maybe used in conjunction with any of the other techniques)

All of these techniques help to get back to the fundamental cause of a defect being injected into a product. TMMi does not dictate which techniques to use, it is for individual organisations to decide which is the most appropriate to use for their defects.

Deployment notes

  • Are defects selected for root cause analysis?

  • Are root causes identified?

Example Sub-practices and work products

Specific Practice 1.3 Analyse cause of selected defects

Perform causal analysis of selected defects to determine their root causes and identify common causes.

Typical work products –

  • Root cause of selected defects
  • Common cause of defects


  • Analyse selected defects to determine their root cause
  • Determine common causes of the selected defects (e.g. process, people, communication, technology)