What is the bus factor and how does it impact delivery?

The bus factor is a relatively morbid term for an older concept called key-person risk, where if a person is hit by a bus and unable to work, then the organisation would be unable to progress their work in their absence. The bus factor (or key-person risk) is a measure of a project, product, or organisation’s dependence on a specific person, to the extent that they’re considered irreplaceable due to their level of experience, skill, or domain knowledge. 

High key-person risk can be unavoidable in the short term, especially in specific circumstances, such as an incredibly high level of domain knowledge or tribal knowledge attained by one person whilst others in the team are relatively new. It can also happen when knowledge of how to use particular tooling is scarce, or if the work being performed is novel to both the organisation and wider industry. 

Delivery teams maximising utilisation of people with the intention of greater delivery throughput can easily fall into the trap of creating silos of knowledge in specific people, unwittingly causing a key-person risk. 

A high bus factor is detrimental during incidents where mean time to recovery (MTTR) would suffer without uninterrupted access to the knowledge and skills of that person. Delivery is additionally negatively impacted when skills and knowledge aren’t ubiquitous within a team, as it puts an artificial constraint on delivery throughput compared to teams where skills and knowledge are common to all.

How to identify the bus factor

If conversations happen within your organisation or team along the theme of “we’ll do this after person Y comes back off holiday” or “we’ll have to wait for Y to be available to fix this” then you’ve got indispensable people with a high key-person risk.

If you desire to increase delivery throughput or reduce MTTR you will need to do work to reduce the key-person risk on those indispensable people.

How to break free from the bus factor

Breaking free from your bus factor will require time and effort – there’s no quick fix! 

Where a key-person risk has arisen because of a knowledge silo around one person (or a very small group), those individuals need to dedicate some time to spreading knowledge amongst their peers. This can be achieved either through active techniques like pairing and mob programming or via more passive actions like documentation and exercises.

An active practice to reduce the bus factor and spread knowledge is to run exercises like chaos days where the people with high key-person risk are the agents of chaos.

Where key-person risk has grown because of the complexity of the work being performed, the process being followed, or the tooling used then significant time and effort must be expended to reduce the complexity. By reducing the complexity, delivery throughput can be increased as more people are able to contribute effort.

Avoiding the bus factor

When a key-person risk is high and there is a desire to actively reduce exposure, using ensemble programming practices such as pairing or mobbing are an ideal way to spread knowledge to the wider team. Training exercises can also be helpful for quickly building basic knowledge amongst larger groups of people.

By virtue of the fact that it involves multiple individuals, mob programming can be the fastest way to spread knowledge and techniques amongst a group. Where pair programming is being used, routinely rotating people into different pairs can ensure system knowledge is maintained amongst the wider team. 

Writing documentation and verifying understanding via exercises will spread knowledge amongst a wider group and acts as a passive reduction in risk exposure where desired.

Final Thoughts

Of course, people are the core of an organisation, but having all your eggs in one basket increases the risk. This is why it’s so important to regularly perform work – be it actively or passively – to spread knowledge and reduce complexity. Doing so will not only reduce the risk of exposure, it will have the added benefit of increasing delivery capacity and reducing mean time to recovery. 

What are you waiting for? Break free from the bus factor now. And if you’ve found this article helpful, share it with your network.