KNOWPIA
WELCOME TO KNOWPIA

**Lusser's law** in systems engineering is a prediction of reliability. Named after engineer Robert Lusser,^{[1]} and also known as *Lusser's product law* or the *probability product law of series components*, it states that the reliability of a series of components is equal to the product of the individual reliabilities of the components, if their failure modes are known to be statistically independent. For a series of *N* components, this is expressed as:^{[2]}^{[3]}

where *R _{s}* is the overall reliability of the system, and

If the failure probabilities of all components are equal, then as Lusser's colleague Erich Pieruschka observed, this can be expressed simply as:^{[2]}

Lusser's law has been described as the idea that a series system is "weaker than its weakest link", as the product reliability of a series of components can be less than the lowest-value component.^{[4]}

For example, given a series system of two components with different reliabilities — one of 0.95 and the other of 0.8 — Lusser's law will predict a reliability of

which is lower than either of the individual components.

**^**Collins, R. (July 14, 2003). "Lusser's Law".*The American Spectator*. Retrieved 10 August 2015.- ^
^{a}^{b}DeVale, J. (1998). "Basics of Traditional Reliability" (PDF). p. 8. Retrieved 11 August 2015. **^**Kopp, C. (1996). "System Reliability and Metrics of Reliability" (PDF). Peter Harding & Associates, Pty Ltd. p. 7. Retrieved 11 August 2015.**^**Critchley, Terry (2014).*High Availability IT Services*. CRC Press. p. 117. ISBN 9781482255911.