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System Dynamics

Age of companies in S&P500
Pradeesh Kumar

​This model attempts to understand the behavior of average lifetime of companies in the S&P500 index. The reference mode for the model is a graph available at this link: https://static-cdn.blinkist.com/ebooks/Blinkracy-Blinkist.pdf (page 5) which was discussed in the System Thinking World Discussion forum.

Mergers & Acquisitions can be one of the reasons for older companies to be replaced with newer companies in the Index. With M&A of older companies, the empty slots are taken over by newer companies. However, overtime, these new companies themselves become old. With steady M&A, the stock of older companies decreases and stock of newer companies increases. The result is that average age of the companies in the S&P Index decreases.

The oscillations in the diagram, according to me, is due to oscillations in the M&A activity.

There are two negative feedback loops in the model. (1) As stock of new companies increases, the number of companies getting older increases which in turn decreases the stock. (2) As M&A increases, stock of older companies decreases which in turn decreases M&A activities.

Limits of the model

The model does not consider factors other than M&A in the increase in number of new companies in the Index. New companies themselves may have exceptional performance which will result in their inclusion in the Index. Changes in technology for example Information Technology can usher in new companies.

Assumptions

1. It is assumed that M&A results in addition of new companies to the Index. There could be other older companies too, which given the opportunity, can move into the Index. Emergence of new technologies brings in new companies.

Business System Dynamics

  • 2 years 2 months ago

C difficile and Whole Genome Sequencing
Amy Buchanan-Hughes
InstructionsAdjust values by using the sliders below or typing in values, then press "Simulate"
To find total cases or total cost with or without WGS, run the simulation twice with WGS = 0 and WGS = 1 (make sure you record the values each time)
Refresh page to restore default values
Warning:Initial proportion of asymptomatically colonised patients + Initial proportion of symptomatically infected patients must be < 1
Proportion of admissions asymptomatically colonised + Proportion of admissions with symptomatic infection must be <1
Email amy.buchanan-hughes@costellomedical.com with queries or comments

Healthcare HCAIs C Difficile System Dynamics

  • 2 years 3 months ago

Oferta y demanda de materiales de construcción en Cali
Scifue
Este modelo busca simular la demanda y oferta de materiales de construcción en la ciudad de Calí (Colombia), En cuanto a la demanda se presenta como principales iniciadores entre otros: La salud económica (PIB regional, desempleo, cartera hipotecaria)Estado de la construcción (Licenciamientos, iniciaciones, obras civiles, despachos de cemento)En cuanto a la oferta se presenta como principales iniciadores entre otros:Capacidad de proveedores: (Disponibilidad de fuentes, Calidad)Aspectos legales (Titulos mineros, socioambiental)Transporte (Flete, estado de la red vial, precio de combustible, distancia de acarreo)

Demand System Dynamics Regional

  • 1 year 7 months ago

Sterman Model (2002)
wmstroup
Based on model discussed by John D. Sterman (p 508) in All models are wrong: reflections on becoming a systems scientist (2002). Task: (A) Sketch what you think the resultant graph will be (see directions for drawing in model). (B) Then Run Simulation.  Optional Extension: Replace Graph In/Out Flow connection with a connection from Trig. function.  Repeat (A) & (B).

Sterman System Dynamics

  • 3 years 11 months ago

The Tyranny of small steps archetype (agent based)
H Haraldsson
A new archetype, The Tyranny of Small Steps (TYST) has been observed. Explained through a system dynamics perspective, the archetypical behaviour TYST is an unwanted change to a system through a series of small activities that may be independent from one another. These activities are small enough not to be detected by the ‘surveillance’ within the system, but significant enough to encroach upon the “tolerance” zone of the system and compromise the integrity of the system. TYST is an unintentional process that is experienced within the system and made possible by the lack of transparency between an overarching level and a local level where the encroachment is taking place.

Reference:

Haraldsson, H. V., Sverdrup, H. U., Belyazid, S., Holmqvist, J. and Gramstad, R. C. J. (2008), The Tyranny of Small Steps: a reoccurring behaviour in management. Syst. Res., 25: 25–43. doi: 10.1002/sres.859 

Agent Based Modelling ABM System Dynamics Archetype

  • 2 years 10 months ago

First SD Model: Predator Prey Model with Squirrels, Mountain Lions, and Hunters
Kate Glassman
At first, I cloned the System Dynamics Model from the "Predator-Prey Interactions" tutorial. After I did this for populations of squirrels and mountain lions instead of moose and wolves, the model showed that the more squirrels mountain lions catch, the more the mountain lion population grows, and the squirrel population declines. The squirrel death rate, therefore, depends on the number of mountain lions and the mountain lion birth rate depends on the number of squirrels. 

I complicated the model by adding 15 hunters to the landscape. Now, the model starts with 150 squirrels, 100 mountain lions, and 15 hunters. This model operates under the assumption that hunters want to kill mountain lions, who presumably try to eat the farm animals that represent the hunters' livelihoods. I made the mountain lion death rate dependent on the number of hunters, and the model changed such that the squirrel population exploded and the mountain lion population approached extinction every 20 years. I based this model on a real event, which took place and is still taking place in the Sierra Nevada. Squirrel populations there apparently reached record levels when farmers seeking to protect their land killed off the vast majority of the mountain lion population there. Now, hunters in the area kill squirrels for sport because they disrupted the food chain so irrevocably.

System Dynamics

  • 1 year 7 months ago

Sterman Model (2002)
Walter M. Stroup
Based on model discussed by John D. Sterman (p 508) in All models are wrong: reflections on becoming a systems scientist (2002). Task: (A) Sketch what you think the resultant graph will be (see directions for drawing in model). (B) Then Run Simulation.  Optional Extension: Replace Graph In/Out Flow connection with a connection from Trig. function.  Repeat (A) & (B).

Sterman System Dynamics

  • 2 years 9 months ago

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