The Bus Factor Islands (BFI) metric is a DETANGLE® Team Collaboration metric based on issues selected by the “Features” filter.

The “Features” filter is normally used to select the issue types which capture the functionality (e.g. user stories or features) as “functional” issues of your system in your issue tracker.

Bus Factor Islands reflects the number of contributors working on their own on an exclusive set of code modules when implementing “Features”. The code modules behind make up knowledge islands.

In addition, the effort of these contributors has to be highly above the average effort of all contributors working on their own on knowledge island code modules.

Losing such a contributor poses a risk since she might be the one knowledgeable of certain parts of the code base only. The lower the BFI number the better, since a low number indicates:

• An even distribution of knowledge islands across contributors and few big knowledge island contributors
• An even split of work effort across all contributors when implementing “Features”.

The Bus Factor Islands % metric measures the percentage of Bus Factor Islands contributors compared to the total number of contributors working on “Features”.

Therefore,  icons in the DETANGLE® diagrams on BFI are used for the following to thresholds:

• 👎 more than 40% of all contributors count up to the current BFI value in the last time period.
• ⚠️less than 40% but more than 20% of all contributors count up to the current BFI in the last time period.
• 👍 less than 20% of all contributors count up to the current BFI value in the last time period.

BFI is calculated along the code structure of the code base, for files, folders, the whole system and for each time period:

Take a look at DETANGLE® Metrics at a Glance for an overview of all metrics.