In assembly plants, random line stoppages cause production variability. For analytic tractability and data availability, researchers commonly assume that the production process possesses the independent increments property (necessary for a process to be Poisson). If the production process has independent increments, then the production in any interval is independent of the production in any other nonoverlapping interval. This property means, for one thing, that the current period’s production is never influenced by previous production periods. Intuition, however, suggests that current production could be correlated to past production-violating this assumption of independence. If production problems persist from one period to the next, then one would expect the production in adjacent time periods to be correlated. Although the independent increments property is often assumed, its validity has not been demonstrated in practice. The authors analyze data from an automotive asembly plant to assess the validity of the independent increments assumption for its production.
