Thinking in Systems Flashcards
What are the three parts of any system?
All systems consist of Elements, Interconnectedness and a function or purpose.
What are Stocks in a system?
A stock is a store, a quantity, or an accumulation of material or information that has built up over time. A stock is the memory of the history of changing flows within the system.
What are Flows in a system?
The change over time of Stocks in the system.
What are the ways in which a Stock can change in a system?
A stock can be increased by either increasing its inflow rate, or by decreasing its outflow rate. A stock can be decreased by either decreasing its inflow rate or increasing its outflow rate. When the inflow rate and outflow rate are the same, the stock is in Dynamic Equilibrium.
Explain the significance of the fact that stocks tend to change slowly?
Stocks change slowly even when the flows into or out of them change quickly. This is because flows take time to flow. The result of this is that stocks serve as buffers on a system – they can be thought of as a kind of shock absorber.
Name an additional benefit of stocks.
Stocks allow inflows and outflows to be decoupled, and temporarily out of balance with each other.
A system behavior that persists over time is usually an indication that ___ is present.
A feedback loop
A feedback loop is..
when changes in a stock affect the flows into or out of that same stock.
Formal definition of a feedback loop
A feedback loop is a closed chain of causal connections from a stock, through a set of decisions or rules or physical laws or actions that are dependent on the level of the stock, and back again through a flow to change the stock.
A balancing feedback loop is..
Balancing feedback loops are equilibrating or goal-seeking structures in systems and both sources of stability and sources of resistance to change.
A reinforcing feedback loop is..
Reinforcing feedback loops are self-enhancing, leading to exponential growth or to runaway collapses over time. They are found whenever a stock has the capacity to reinforce or reproduct itself.
Doubling Time on an exponentially growing stock
The time the stock will take to double is approximately 70 divided by the growth rate. For example a stock that grows at a rate of 10% a year would take 7 years to double.
Example of systems thinking in real life (feedback loops)
If A causes B, is it possible that B also causes A?
Explain a thermostat as a system.
