Systems Thinking

Systems thinking can be a unifying theme amid this complexity and shifting frames of reference.  The same tools, like behavior over time graphs and feedback loops, can be used across disciplines.  For example, the iterative process of revision and improvement based on feedback is common to virtually all academic subjects, including both the writing process and the design cycle.  Guiding students to recognize these generic traits of thinking and working can help us all become better at interdisciplinary learning.  Take a look at the “Habits of a System Thinker” – you will recognize most of the habits as core values  or desired behaviors in your life.

Another universal principle of systems thinking involves stocks and flows.  Stocks are accumulations of things, and flows measure the rates at which the stocks change.  In a similar way to the introduction of other tools, simple examples of stocks and flows may not add much insight to our understanding.  Water in a bathtub is a common example of a stock.  The flow from the faucet is an inflow that fills the tub, while the drain is an outflow to empty it.  The software named STELLA that we use at IACS draws clear maps of stocks and flows:

No big insight there.  The clouds on the ends of the flows mark the model boundaries.  While it’s important where water comes from to fill the tub and where it travels when it drains, we are not modeling that larger system in our diagram.  This is a simple bathtub map.

But stock and flow thinking becomes difficult for us when the rates of change are confusing.  Let’s substitute other names for the elements in our diagram:

Most people agree this causes a big problem, climate change.  Projections of energy use point out how stubborn the inflow is.  We are essentially running the faucet with the drain open, but the inflow is outpacing the outflow.  If we level off our CO₂ emissions somewhere close to current levels (a giant challenge), the inflow will still exceed the outflow.  And when inflow > outflow, the stock increases.  That’s true for water in a tub, CO₂ in the atmosphere, organisms in a population, happiness in our lives … anything we can represent as a stock and flow.  To reduce the level of CO₂currently in the atmosphere, the rate of removal must exceed the rate of additional CO₂ being produced.

Here’s one more stock and flow map to consider:

If we spend more than we can pay, our stock of debt rises.  But I suspect you know this isn’t the whole story, especially if you’ve borrowed money.  Debt costs us money in the form of interest, and STELLA uses two more icons to complete this picture:

Interest payments are based on a rate represented by a circle called a converter.  The interest rate is multiplied by the existing debt, adding to the stock of debt. This feedback connection is shown by the red arrows called connectors.  Students can easily learn how to input numbers and equations in order to model this situation, learning some important lessons before getting their own credit cards.

Most people benefit from the discipline and practice necessary to draw stock and flow maps.  Their simplicity and clarity of design provide another communication tool representing how a system operates.  We help students gain an appreciation for rates of change, feedback, and other elements of systems when we integrate stock and flow thinking in our curriculum.

If you use any of the activities in The Shape of Change, have a look at the section in the newer editions of the text or on the web to see stock and flow explanations of each activity.

http://clexchange.org/cleproducts/shapeofchange_lessons.asp

“Feedback loops control a system’s major dynamic behavior. A feedback loop is a series of connections causing output from one part to eventually influence input to that same part.”

1. Think about a performance improvement loop, or virtuous circle.  Practice some skill, such as playing music or athletics, and we get better.  When we get better, we can perform at a higher lever, and we can get even better.  Unfortunately, vicious cycles exist also, like inflation.  Prices go up, so workers negotiate higher wages.  Higher wages increase buying power, but companies raise prices as it becomes more expensivve to produce goods, partly because of increased wages.  In systems language, these up or down spirals are called reinforcing loops.
2. Let’s look at performance in a different way.  What if I don’t care about getting better at my lessons?  But my parents care and apply pressure to me.  So I practice and I get better. Once I satisfy them however, I can back off on practicing.  Then my skills begin to erode. That makes my parents react, so I have to increase practice again. I stay with this oscillating pattern, practicing enough to keep my parents off my case, but not working so hard that I forego other activities I’d rather do.  This “wave-like” pattern is a balancing loop.  A thermostat is a good example of a balancing loop in our everyday life.  Heating or cooling is called for when a certain temperature criterion is passed.  Once it is met, the machine doing the work shuts off, until the measure of heat in the room turns it on again .