This is a rare “lean geek” post so for those of you who read for entertainment or diversion, please feel free to surf on and enjoy your weekend. To those of you for whom “data box”, “change loop” and “future state map” are pleasing sounds, please read on.
Yesterday I came across an example of a value stream whose numbers left me puzzled. The value added percentage was greater than 100. This seemed impossible at first but I now understand how it can happen. The process, the numbers and the details in the illustration above have been changed to protect the client’s privacy but the essence of the situation is the same.
In this example a there are three processes, each staffed by a 5 person team of physicians. They work in a continuous flow fashion for 30 minutes per process before moving the patient on to the next process. For the sake of the example and to make it close to the actual example from this week we will say that 20 minutes of the 30 minute cycle time is value added time, and also that the time is divided evenly between the 5 physicians such that the elapsed process time for the patient is 6 minutes (30 min / 5 physicians = 6 minutes). The lead time through process #1 is 6 minutes, while the value added time is 20 minutes. Processes #1, #2 and #3 have identical staffing and times for the purpose of this example. There is a 1 minute patient transport time between processes 1 and 2 and also between 2 and 3 which adds a total of 2 minutes to the lead time.
Totaling the numbers we have 20 min + 20 min + 20 min value added time = 60 minutes value added, and 6 mins lead time + 1 minute waiting + 6 mins lead time + 1 mins waiting + 6 min lead time = 20 mins lead time. Dividing 60 minutes of value added time by 20 minutes of lead time gives us 3 or 300% value added percentage.
The question I would like to pose is, “Does the value added percentage has any meaning for processes which allow for multiple actors (such as people or machines) to add value simultaneously to a single work piece (in this example the patient), and if it not does the value added percentage itself have any validity as a measure foe effectiveness of discrete, single-actor processes?”