Subject: Is this a causal loop?

Posted by Steve Kipp on 2/27/2004
In Reply To:Is this a causal loop? Posted by Della Robertson on 1/27/2004

Message:

Della- I'm also having a tough time seeing these as causal loops for reasons similar to those expressed by John. But I'd like to address your second question, "What is the connection between the loop and the model?" (I assume by "model" you mean "stock/flow model or "computer model"...is that assumption OK?). I think the answer depends on what system you are studying and what the purpose of the study is.

For example, if I want to share my mental model that the relationship between Angry Thoughts and Angry Feelings is one of reinforcing feedback, I can express this as a reinforcing causal loop, and we can explore leverage points. Interestingly, the vast majority of kids will say that it's easier to directly, by act of will, reduce Angry Thoughts than to reduce Angry Feelings (you can sometimes consciously switch what you are thinking about, but it is really hard to just turn off emotions), and reducing Angry Feelings then spins the reinforcing loop down, in effect reducing both. Good leverage point! When we explore the thinking of the few students who say Feelings are easier to directly reduce by act of will, it's usually because they are intuiting this balancing loop: it is their strong feelings which compel them to take physical action, which directly reduces their feelings. But this introduces another variable (physical action), so we add a balancing loop between Angry Thoughts and Physical Action. Nice little practical system, no stock/flow detail necessary, lots of leverage, and potential to teach the concept of loop dominance.

BUT, if you try to explore the reinforcing feedback relationship between "Money in the Bank" and "Annual Interest Payments", causal loops can only take you so far. If you set these two variables up as a simple reinforcing loop, and add "Interest Rate" sitting outside the loop but connected to "Interest Payments", it works until for some reason the interest rate drops. Then the logic of the loop makes it look like the subsequently reduced Interest Payment would make the Money in the Bank go DOWN, when in fact it still goes up but at a lesser rate. Stocks and flows to the rescue! If you set this up as a stock of Money in the Bank, with inflow of Interest Payments, driven by connectors from Money in the Bank and a converter called Interest Rate, you still show the reinforcing feedback relationship between Money in the Bank and Interest Payments, without the confusion of the same system expressed as a causal loop. Does that help?

Steve
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"Tap into the benefits of differences"- Kali Saposnik
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Steve Kipp
Waters Foundation Systems Thinking Mentor Glynn County School System Brunswick, GA

Follow Ups:

Is this a causal loop? - John Gunkler 3/9/2004 
Is this a causal loop? - Steve Kipp 3/11/2004