Average items in a system equal arrival rate times average time in it, so at fixed throughput less work in progress means shorter lead time.
Little's 1961 theorem holds in a stable system regardless of distribution or scheduling discipline: average work in process equals throughput times average time in system. At fixed throughput, reducing average work in progress reduces average lead time.
In practice
- A team with sixty tickets in progress and four finished a week has a fifteen-week lead time, whatever anyone plans.
- A clinic that books forty patients into a queue with a two-a-day discharge rate has a twenty-day wait by arithmetic alone.
- Further reading
- Wikipedia
- Subject
- Design & Systems
- Essay
- The limits every design runs into