Causal Loop Diagramming (Part 2)

In the previous post, a basic understanding of Systems Thinking was provided and an introduction to Casual Loop Diagramming (CLD) with the most common notation explained. This post will cover additional CLD notation and expand on our real world example (i.e. why I eat too much, sometimes 😯 ). The notations covered will be goals, extreme effects, constraints, interaction effects, and feedback cycles.

Let’s review the current state of the example. We had two variables, “Degree of Hunger” and “Amount of Intake.” With the causal links illustrated below. Based on the diagram, one could say as, “my degree of hunger goes up, the amount of food I intake will go up. Then as the amount of food I intake goes up, there will be a delayed effect on my degree of hunger going down.”

CLD of Human System


Many systems have goals. It is worthwhile to incorporate these into our diagram because they can have significant impacts, either positive or negative. Let’s add one to our example. Summer is coming, I would like to have a Body Mass Index (BMI) of 21.5. 😀

Goals can be represented in a CLD similar to a variable but with a different color. Green usually works well.

Goal Added

Let’s also add “Level of Stress,” “Body Mass Index,” and “Gap Between Goal and Current” to our model.

Added Level of Stress, BMI, and Gap

This now represents my stress level rising as the gap between my BMI goal and current BMI goes up. 🙁

Extreme Effects

Sometimes, extreme effects occur on one or more of the variables in the system. It is helpful to highlight these when they exist because they can have significant impacts. Extreme effects are drawn as a thick line between two variables. In our example let’s parse out the “Amount of Intake of Food” into “Amount of Intake of Comfort Food” and “Amount of Intake of Healthy Food”

Split Intake into Comfort and Healthy Foods

For me, when my level of stress rises, I tend to seek even more comfort foods. This has been highlighted by labeling this link as an extreme effect.


Most systems have constraints that cause limitations. Constraints can be represented similar to variables but with a different color. Blue usually works well. Also add the letter “C” on the link that is constrained. In the example add “Cash Supply” as a constraint.

Add Cash Supply Constraint

Interaction Effects

The “Cash Supply” will not affect a specific variable but does effect some of the causal links in our system. This is an example of an interaction effect on the system. This doesn’t effect a variable directly but can have an impact on the effect one variable has on another. The interaction effects have been added to the cash supply constraint in the example.

Interaction Effects of Cash Supply

When interpreting this addition to our example, one might read it as “a decrease in cash supply can increase the effect level of stress has on the amount of comfort food I eat.” I probably won’t have healthy snacks laying around because they are usually more expensive.

At this point, the most common Causal Loop Diagram (CLD) notation has been introduced. The example is a good start. It is by no means complete. There are many more variables we could introduce to make this a more realistic model. Some might be, “Ability to Cope with Stress in a Healthy Way,” “Level of Happiness,” or “Level of Sleep.”

Feedback Cycles

The current state of the diagram does allow us to identify feedback cycles that can be either virtuous (positive) or vicious (negative). This is where the magic of CLD comes out.

To identify feedback cycles, trace the links to make a loop. This can be a little challenging when first getting started analyzing CLD’s. Once a loop is identified, a positive/virtuous feedback cycle is any that has an even number of opposing causal links. The alternative is the negative/vicious feedback cycle. Let’s highlight this one first in our example.

Negative Feedback Cycle

One can read that there is a vicious cycle where one variable (i.e. Level of Stress) going up causes all the other variables (i.e. Amount of Intake of Comfort Foods, BMI, and Gap Between Goal and Current) to go up as well. Yikes, now it is clear to me that I need to stop this vicious cycle.

How could this be fixed? Maybe I should just make my BMI goal, 25, but that isn’t going to work for me on the beach. How about figuring ways to lower my stress level. That seems like a great place to start. Maybe I could try meditation, exercise, yoga, reducing my workload, playing with Legos, knitting hats (probably not), etc…

There is one positive feedback cycle in our example.

Positive Feedback Cycle

One can read that despite my stress level, I can work hard to intake healthy foods that should cause a drop in my BMI and allow me to close in on my goal. This still requires action from me. I think I will need to improve my ability to cope with stress in a healthy way. The stress reducing activities above could probably be useful as well.

Now go out and put this tool to work for you and your colleagues/friends. Try using it with either professional or personal struggles. Some good examples might be: why did I not get promoted, why am I not satisfied with my job, why do I spend more than I make, why do my kids misbehave, etc…

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