background image
<< Software Defect Reports | Testing Metrics for Developers >>

Root Cause Analysis

<< Software Defect Reports | Testing Metrics for Developers >>
Root Cause Analysis
Root cause analysis is the identification of the root cause of a defect.
Basic root cause analysis can often be extremely illuminating if 50% of your software defects are
directly attributable to poor requirements then you know you need to fix your requirements
specification process. On the other hand if all you know is that your customer is unhappy with the
quality of the product then you will have to do a lot of digging to uncover the answer.
To perform root cause analysis you need to be able capture the root cause of each defect. This is
normally done by providing a field in the defect tracking system in which can be used to classify
the cause of each defect (who decides what the root cause is could be a point of contention!).
A typical list might look like this :
The defect was caused by an incomplete or ambiguous requirement with
the resulting assumption differing from the intended outcome
Design Error
The design differs from the stated requirements or is ambiguous or
incomplete resulting in assumptions
Code Error
The code differs from the documented design or requirements or there
was a syntactic or structural error introduced during coding.
Test Error
The test as designed was incorrect (deviating from stated requirements or
design) or was executed incorrectly or the resultant output was incorrectly
interpreted by the tester, resulting in a defect "logged in error".
The defect was caused by incorrectly configured environment or data
Existing bug
The defect is existing behaviour in the current software (this does not
determine whether or not it is fixed)
Sub-classifications are also possible, depending on the level of detail you wish to go to. For
example, what kind of requirement errors are occurring? Are requirements changing during
development? Are they incomplete? Are they incorrect?
Once you have this data you can quantify the proportion of defects attributable to each cause.
In this table, 32% of defects are attributable to
mistakes by the test team, a huge proportion.
While there are obviously issues with
requirements, coding and configuration, the
large number of test errors means there are
major issues with the accuracy of testing.
While most of these defects will be rejected
and closed, a substantial amount of time will
be spent diagnosing and debating them.
This table can be further broken down by other defect attributes such as "status" and "severity".
You might find for example that "high" severity defects are attributable to code errors but "low"
severity defects are configuration related.
A more complete analysis can be conducted by identifying the root cause (as above) and how the
defect was identified. This can either be a classification of the phase in which the defect is
identified (design, unit test, system test etc.) or a more detailed analysis of the technique used to
discover the defect (walkthrough, code inspection, automated test, etc.) This then gives you an
overall picture of the cause of the defect and how it is detected which helps you determine which
of your defect removal strategies are most effective.
Design Error
Code Error
Test Error
Existing bug
Figure 14: Sample root cause analysis