Systems react to external events but behavior is entirely dependent on the internal workings of the system. That’s important because changing behavior can only come from changing the system.
System structure and behavior
Systems are interconnected sets of elements coherently organized that achieves something. It’s not a system of the elements aren’t interconnected. It’s not a system of it doesn’t do anything.
Elements are the easiest to recognize and are often tangible (e.g. a tree has branches, roots, a trunk, leaves, etc.). However it’s easier to Leanne about a system’s elements than its interconnections.
The function or purpose of a system is harder to recognize because it is often unwritten. The best way to discover the systems function is to deduce it from behavior not what it says it does.
An important function of every system is to perpetuate itself.
Elements, interconnections, and functions—in that order—have the largest effect of change in a system. For example, change all the players on a football team and it still functions as a football team, change the rules of the game and it becomes basketball, change the function from winning to losing and it’s unrecognizable.
Stocks are the present memory of the history of changing flows within the system like the meandering of a river from centuries of floods and droughts. Stocks is a countable unit that changes through the action of a flow. Dynamics of stocks and flows is their behavior over time.
Example: filling a bathtub shows you inflows (the faucet) outflows (the drain) stock (the water in the tub) and their dynamics (turning down the faucet lowers the water level in the tub, turning up the faucet increases the water level,
matching rate of water from the faucet to the drain rate results in equilibrium)
People seem to focus more easily on stocks and inflows over outflows. This leads to cognitive error because a system might be better off achieving its goals by altering the outflows than the inflows (e.g. decreasing oil usage by finding new energy sources rather than finding new oil deposits).
A stock takes time to change even with sudden changes to inflows and outflows much like filling or draining a bathtub isn’t instantaneous. This has a stabilizing effect that is often underestimated. Flows take time to flow. Forests don’t grow overnight.
Stocks and flows are decoupled. You don’t go to the bank to take out money every time you want to buy something. Most decisions made by individuals and institutions have to do with regulating levels of stocks.
Feedback loops can be observed as controls of a stock, despite increases and decreases. For example, if your bank account balance goes down (stock), you reduce spending (outflow) to keep the balance within an acceptable range. It is a closed chain of causal connections through a decision/rule/law/action dependent on the stock that affect the flow of that stock.
A balancing feedback loop is goal seeking or stability seeking—a “homing” pattern of behavior. It opposes whatever direction of change is happening (high -> low, low -> high) to maintain a stock within a range of values.
A reinforcing feedback loop generates more input to a stock the more is in there. This is a vicious/virtuous cycle. For example, prices go up the more wages go up so to maintain profits prices must go up and so on. This happens anytime a system element has the ability to reproduce itself or grow at a compounding rate.
It’s useful to think not just about A causing B but about how B causes A. It helps you think about systems and how that explains its behavior.
One stock with two feedback loops (a thermostat)
A flow can’t react instantly to a flow. That’s why a thermostat won’t hold the temperature steady if the heat leaking to the outside is too high and you need to set it higher than the temperature you want to counteract it. By the time the heat is pushed into the room, it leaks out at a higher rate so the two loops compete and cause the room temperature to fall.
A stock with one reinforcing loop and one balancing loop (births and deaths effect in population)
Shifting dominance is when one loop has a larger impact than the others. For example, when fertility rate is high, the reinforcing loop of births is dominant and so population grows. When fertility rate falls, the mortality loop is dominant causing more deaths than births.
When evaluating a model, ask:
- Are the driving factors likely to unfold?
- in they did would the system react this way?
- What is driving the driving factor?
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