Variation Continued
Action taken when common cause variation is treated as
if it were assignable cause variation is called tinkering.
Tinkering actually increases the variation in the system
because the system is adjusted based on random
changes in system performance. Taking action to adjust
the system when such action is not warranted can be
just as detrimental to system performance as failing to
take action when such action is needed to correct an
This can be demonstrated with the funnel experiment