From www.controlchaos.com 
( Broken Link )
Models of empirical processes are derived categorizing observed inputs and outputs, and defining controls that cause them to occur within prescribed bounds. Empirical process modeling involves constructing a process model strictly from experimentally obtained input/output data, with no recourse to any laws concerning the fundamental nature and properties of the system
The Scrum Process, and other Agile Processes, use an empirical process control model instead of a Defined Process control model. This means that they depend on Inspect And Adapt cycles, instead of phases, hand-offs, sign-offs and blame.
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