Defect Clustering

In most cases, it can be seen that the majority of the detected defects are caused by a small number of modules, i.e. the distribution of defects are not across the application but rather condensed in particular areas of the application. This is particularly true for enterprise systems where the complexity, size, continuous change and developer inexperience can impact the quality of the system and affect particular modules.

This analogy is based on the Pareto principle, also known as the 80-20 rule, where it is stated that approximately 80 per cent of the problems are caused by 20 per cent of the modules. This can give a good indication that when a defect is found in one area of the application, chances are there are more defects in that particular area, so it is worth investing more time to test that particular area of the application to find as many defects as possible. However, this should not deter testers to “ignore” the rest of application as there may be other defects scattered around