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Reinforcing and Balancing Behavior Lab

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About This MicroSim

A causal loop diagram shows the structure of a system. This lab shows the behavior that structure produces. It runs the two update rules from Chapter 8 side by side, one time step at a time:

  • Reinforcing loop (R, red circles): x = x + rate * x. The change each step is proportional to the current value, so growth feeds more growth and the curve bends upward.
  • Balancing loop (B, green squares): x = x + rate * (goal - x). The change each step is proportional to the distance from the goal, so the curve rises quickly at first and then levels off at the dashed goal line.

Both curves share the same rate and start value, so any difference you see comes from the loop structure alone. The vertical axis always runs from 0 to twice the goal, so the goal line sits at mid-height; when the reinforcing curve leaves the top of the chart, a marker shows the step where it escaped. A caption under the chart explains the shape seen so far with the actual numbers, for example "B is slowing: next step adds 0.10 × gap 34.9 = +3.5".

With Predict first turned on, the lab pauses each time you move a slider and asks whether each curve will rise faster, slower or the same over the first 10 steps, compared with the previous settings. The previous run stays on the chart as faint dashed curves, and after step 10 the lab reports each result with the two rises. The most revealing change is the start value: a higher start makes the reinforcing curve rise faster but the balancing curve rise slower, because the balancing loop responds to the gap, not to the value.

Learning objective: The learner will compare the time behavior of a reinforcing loop and a balancing loop by changing the loop rate and the goal and observing the resulting curves.

Bloom's taxonomy level: Understand (verb: compare)

How to Use

  1. Press Start and watch both curves grow for 50 steps. Read the caption as they grow.
  2. Hover over any point to see its step number and exact value.
  3. Move one slider: Rate (0.01 to 0.30), Goal (50 to 200) or Start value (1 to 50).
  4. With Predict first checked, choose Faster, Slower or Same for the R curve and for the B curve. The run starts when both predictions are in, and the panel (or the caption on narrow screens) reports whether you were right, with the rise over the first 10 steps before and after your change.
  5. Press Reset to clear the prediction state, or uncheck Predict first to explore freely.

Iframe Embed Code

You can add this MicroSim to any web page by adding this to your HTML:

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<iframe src="https://dmccreary.github.io/microsims/sims/feedback-behavior-lab/main.html"
        height="652px"
        width="100%"
        scrolling="no"></iframe>

Lesson Plan

Audience

Teachers, instructional designers, learning-technology developers and learning-analytics practitioners (college undergraduate and professional development). No prior system dynamics background is assumed.

Duration

15 to 20 minutes

Prerequisites

  • The definitions of a feedback loop, a polarity link, a reinforcing loop and a balancing loop (Chapter 8, "Systems and Feedback")
  • Reading a line graph with time on the horizontal axis

Activities

  1. Observe (3 min): Run the default settings (rate 0.10, goal 100, start 10). Describe the shape of each curve in one sentence, using the words "accelerating" and "leveling off".
  2. Predict and test (7 min): With Predict first on, make three single-slider changes: raise the rate, raise the goal, then raise the start value. Record each prediction and result in a table with columns for the change, R and B.
  3. Compare (5 min): In pairs, explain why raising the goal changes the B curve but not the R curve, and why raising the start value speeds up R but slows down B. Use the two update rules in your explanation.
  4. Connect (3 min): Relate each curve to the learner loops from the chapter: Mastery, Confidence and Practice time (R1), and Gap, Study effort and Mastery (B1). Which one describes a learner who is catching up to a fixed learning goal?

Assessment

  • Given a new setting, the learner predicts correctly whether each curve will rise faster, slower or the same, and justifies the prediction from the update rule.
  • The learner states the difference in one sentence: a reinforcing loop changes in proportion to its current value, while a balancing loop changes in proportion to its distance from a goal.
  • The learner identifies which loop type produces goal-seeking behavior and which produces exponential growth or decline.

References

  1. System dynamics - Wikipedia. The field that studies how stocks, flows and feedback loops produce behavior over time.
  2. Causal loop diagram - Wikipedia. Explains reinforcing and balancing loops and the sign-counting rule.
  3. Exponential growth - Wikipedia. The behavior of a pure reinforcing loop, where the growth rate is proportional to the value.
  4. p5.js createSlider() reference - p5.js. The built-in slider control used for the rate, goal and start value.