The length of stay can be affected by an increase of decrease in arrival rates of patients and using this as a single metric may not provide the insight needed to determine process improvements. Even though length of stay remains unchanged other metrics can indicate performance improvement. Since there is a relationship between length of stay, the average number of patients and throughput, we must look at all indicators to effectively measure improvements. For example, the time spent waiting or throughput of the system will indicate possible improvements. Patients value short waiting periods before entering the system, and a reduction in this queue is a good indicator of improved patient flow. Thus, pinpointing improvement in patient flow by using only length of stay can be deceiving.
The example below demonstrates a situation where the flow time remains the same however the throughput of the system has improved. For this to happen, the average number in system (average inventory) needs to increase by a proportional amount. Given that this situation uses the same resources and arrival rates are equal, we can conclude there has been a process improvement.