One of the process failures we identified in our nature of work discussion was the process flow failure of unnecessary wait times or delays. When we look at a value stream map of a process our focus is the movement of the product or service through each step until it reachs the customer. The ideal flow is a single piece and continous flow of work that moves seamlessly through to completion. A simple way to numerically quantify what we identify on our value stream map, we can calculate our process flow or efficiency. Process flow or efficiency is equal to the value added time divided by the process cycle time. Value added time is the time it takes to complete the process from the first step to the last without interrruption or rework ( the "ideal") . This may be depicted in our "as should be" value stream map. The process cycle time is the actual time it takes to complete the process steps including wait times and rework.
For an example of calculating process efficiency consider the process flow below;
- A patient at the hospital has had a breast biopsy performed and waits anxiously for a diagnosis
- The patient waits for scheduled procedure appointment= one week (40 business hours)
- Time to perform the test = 1 hour (value added)
- Preparation of the biopsy = grossing 10 minutes + tissue processing 8 hours
- Reading of the test result = 20 minutes
- Report generated and sent to clinican = 12 minutes
- Clinician meeting with patient and explaining the diagnosis= 10 minutes
Value Stream Results for Patient Biopsy Procedure
Value added = 11 minutes (procedure and face time with the clinician)
Non-value added = 49 hours and 42 minutes
Process flow efficiency = 11/49.42
This process has only a 22.2% efficiency!
Part of the bottlenecks and wait times in the above example are related to departmental organization and also to the batching of processes. In our example above, batching of tissue into one long processing run which is completed over-night has added 8 hours and 10 minutes of wait time for the patient.
To some extent flow thinking is counterintuitive when we are very familiar or accustomed to a process. However being able to step back and look at our processes through the customer's eyes is the key to eliminating bottlenecks, back flows, and non-value added activity.