Process variation is the
main course of quality problems, whether
in business (transactional) or production
processes. The main task of statistical
process improvement methods such as Statistical
Process Control, Six
Sigma and Measurement
Systems Analysis and the
Taguchi approach
to Experimental Design is to control
and reduce process variation.
Process variation and process precision
are closely related. A process with little
variation is said to be 'precise'. When
studying process variation it is important
to make a clear distinction between process
accuracy and process precision. A process
that is 'accurate'
may not be 'precise' and a process that
is 'precise' may not be 'accurate':

Not
Precise 
Precise 
Not Accurate



Accurate 


Most processes are designed with controls
that can be used to adjust the process mean,
and hence increase the accuracy. Reducing
the amount of process variation is usually
more difficult.
