In business management, and especially in the field of software development, is
a measurement of the concentration of information in individual team members.
It is also known as truck factor, or bus/truck number or lorry factor.
Definition A project's bus factor is the number of
persons it would need to lose in order for the project to lose its
institutional memory and halt its progress. The bus factor is a
measurement of the concentration of information in individual team members.
A high bus factor is considered a good thing as it means that many individuals
know enough to carry on and the project could still succeed even in very adverse
events. "Getting hit by a bus" could take many
different forms where the project would retain information with which no
remaining team member is familiar, including anything that suddenly and
substantially prevented the individual from working on the project. This could
be a person taking a new job, having a baby, changing their lifestyle or life
status: the effect would be the same. = Alternate definition =
A rare alternative defines the bus factor as the number of persons who are
indispensable for the project. In other words, it is the number of persons who
are a single point of failure. If using this definition, then a high bus factor
is considered a bad thing, and zero is considered the ideal bus factor.
History In 1907, Joseph Conrad wrote in "The
Secret Agent": But just try to understand that it was a
pure accident; as much an accident as if he had been run over by a 'bus while
crossing the street. "Truck number" was already a recurring
concept in the Organizational Patterns book published in 2004, itself an
evolution of the work published in the first book of the Pattern Languages of
Program Design series in 1995, which was the publication record of the first
Pattern Languages of Programs conference in August 1994, where it was referenced
in patterns including Solo Virtuoso. The term had become commonplace in business
management by 1998 and was used in mental health in the same year. It was
seen in software engineering papers in Association for Computing Machinery and
Information Systems Frontiers by 1999, in engineering by 2003, and the Debian
project in 2005. An early instance of this sort of query
was when Michael McLay publicly asked, in 1994, what would happen to the Python
language if Guido van Rossum were hit by a bus.
A July 2015 study calculated the bus factor of 133 popular GitHub projects.
The results have shown that most of them have a small bus factor and the value is
greater than or equal to 10 for just seven systems.
Increasing the bus factor Several ways to increase the bus factor
have been proposed: Reduce complexity,
Document all processes and keep that documentation up-to-date,
Encourage cross-training. References
^ Bowler, Michael. "Truck Factor". Agile Advice.
^ James Coplien, Pair Programming Illuminated. Quote: "How many or few
would have to be hit by a truck before the project is incapacitated?"
^ Coplien, James; Harrison, Neil. Organizational patterns of agile
software development. Wiley. ^ Coplien, James; Harrison, Neil.
Organizational patterns of agile software development. Wiley.
^ Coplien, James; Schmidt, Douglas. "Chapter 13, A Generative
Development-Process Pattern Language". Pattern Languages of Program Design.
Addison Wesley. ^ Coplien, James, "A Generative
Development-Process Pattern Language", Internal proceedings of PLoP 1994,
Allerton Park, Illinois: unpublished. ^ Simon, Robert. The Mental Health
Practitioner and the Law: A Comprehensive Handbook. Harvard
University Press. p. 69. ISBN 0-674-69721-9.
^ Redmond, Matthew C.; Newton, Paul. "Integrating GIS in the Engineering,
Planning and Design Processes". ^ Reinholdtsen, Petter. "Re: Resignation
and uploads". ^ McLay, Michael. "If Guido was hit by a
bus?". ^ Avelino, Guilherme; Valente, Marco
Tulio; Hora, Andre. "What is the Truck Factor of popular GitHub applications? A
first assessment.". PeerJ Preprints. ^ a b c
s.com09increasing-your-teams-bus-factor/ Further reading
Michele Marchesi, Giancarlo Succi, Don Wells, James Donovan Wells, Laurie
Williams. Extreme Programming Perspectives. Boston u. a.:
Addison-Wesley. ISBN 0-201-77005-9. Laurie Williams, Robert Kessler. Pair
Programming Illuminated. Boston u. a.: Addison-Wesley. ISBN 0-201-74576-3.
Kent Beck. Extreme Programming. Das Manifest. s. l.: Addison-Wesley. ISBN
3-8273-2139-5. External links
Poisonous People, a talk that includes discussion of bus factor and how to
increase it