By Julián Chacón
Currently in Nijmegen, Netherlands
European Master in System Dynamics, Class 2013-2015
The “SD bible man” during the workshop (as tagged by student Nikola Pucarevic during his live social media updates on the conference)
My experience in the summer SD conference in Delft was of great importance for me, since it introduced me to many people that are working in the field already and it enhanced my network development for my short term work, but also for the mid and long term. I again convinced myself that I am in the right place with a powerful tool, but also that I need to learn other tools to complement my competencies and be able to model our world.
On the human side, I think that the mood and kindness of the people involved in the conference were really nice, and since I was a newcomer, everyone tried harder to make me comfortable. I appreciate this and feel thankful about it.
I could write quite a lot about some of the presentations that had a positive impact on me, from Rogelio Oliva stirring us up about submitting to the SD review, to Kim Warren’s easy way of sharing his knowledge and experience, but also through some of the young practitioners that have been doing a high level System Dynamics work; but there was one presentation that in particular touched me in a certain way. Maybe it has to do with the fact that he is one of the “gurus” of the field, and his book is one of the main references I have been using in my master’s program, but the way he presented his speech was very special for me. His name, if you have not guessed it already, is John Sterman.
John started his presentation talking about the all-famous beer game and about some of the criticism it has received about being unrealistic in its assumptions (in particular, the step change in the final consumer demand). In order to try to answer to some of these criticisms and for the sake of improving the modelling practice, he revisited the beer game, but now leaving the final demand without a change, i.e., remaining constant.
And here is why his presentation was so special for me. Besides the fact that he is so easy in his presentation and way of talk (I could never see Richard Feynmann, a theoretical physicist, but I read a lot of things about him, and I think that John could be the Feynmann of System Dynamics), the structure of his presentation was that of the state of the art.
He presented his new assumption (constant demand), then used the same structure of a supply chain that works on demand with inventory coverage, and then presented the equations that would represent the relationships between the different elements of the system (his hypothesis). He developed his hypothesis, and after doing some analysis he kept forward, but then it was time for the experiment for proving his hypothesis, and in this point is where I really enjoyed what he did and what was the conclusion he got from it. The experiment consisted of playing the beer game (under controlled conditions) to see if his hypothesis was still valid. He made the experiment changing the information given to the participants a little bit so he could tell more about the expected behavior that his model would represent.
In particular, he told everyone that the demand would not change at any moment, so he would expect that everybody ordered the same amount each time, since there was no suspicion about any change in the ordering. But what was his surprise when he found that this was not true, since there were some persons that order quite a lot at the beginning even if they knew that the demand would not change at any time. Then, he entered to the psychology field to try to understand what was going on, and he found out that there was a syndrome associated with accumulating goods originated from certain factors, but that also has its physiological origin in the brain, these guys are called “accumulators”. So, since these accumulators were not represented in his model, then his hypothesis had to be changed, i.e, his hypothesis was not valid anymore.
Wow, it was a demonstration of how an abstraction that we made from reality, was developed in our mind, formalized with mathematics, analysed with our tools, and then proven with what we can tell about the reality (with the experiments with the subjects involved in our models, i.e. humans) and find out if it could work. Absolutely amazing. This combined with his so fresh way of telling his story made the perfect combination for his presentation.
After his presentation, I stood up, and kept thinking for a while on what I had just seen. It gave me more clarity on some of the ideas that I have for my work, but also brought more questions on how I should proceed with it. The next day, I was eating with a colleague and then I saw John just in front of us. I immediately asked him for a picture with me, and without hesitating, he left his dish aside, and stood by my side for the picture. With a big smile and a big mind, that humble man gave me a picture and a thought that will remain forever in my life.
One of the great moments of meeting inspiring people
Would you like to learn more? Consider the following links:
The Beer Game
John D. Sterman
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