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From SystemsWiki

Have you ever thought about why when you fill a glass with water you seldom overflow it, or why when you get near the end of a project the final portion seems to take so much longer than it should? What you're experiencing is the effect of a balancing loop in operation.

In this segment we're going to create a generic version of the Balancing Loop, investigate it a bit deeper and then consider some of the potential ways in which this simple structure might evolve into more complex structures, also representing Systems Archetypes.

Contents 1 Causal Loop Diagram 2 Stock & Flow Diagram 3 Simulation 4 Effective Strategies 5 Areas of Concern 6 Examples 7 References

[edit] Causal Loop Diagram

Fig. 1 presents a Causal Loop Diagram for the generic Balancing Loop. The assumption here is that the desired state is greater than the current state. As such, the gap is the difference between the desired state and current state. The gap adds to the action moving the current state toward the desired state. The current state subtracts from the gap. When the current state reaches the desired state the gap becomes zero and there's no more action.

[edit] Stock & Flow Diagram

Fig. 2 presents the Balancing Loop as a Stock & Flow Diagram with the Current State represented as a stock which only changes through the flow of action.

Note that the source of the action is not considered to be relevant to this model and is represented by a cloud. And the % change factor simply controls the rate at which the gap influences the action.

[edit] Simulation

While you might consider just opening the Project Completion model from the prior module, creating it from scratch should only take a few minutes, and the practice is also a good thing. So, create a model that looks like the Balancing Loop in Fig. 2.

 

To create the above diagram:

• Create a Stock and name it Current State
• Create a Flow, name it action and connect it from none to Current State
• Create a Parameter and name it gap
• Create a Link from gap to action
• Create a Link from Current state to gap
• Create a Parameter and name it desired state
• Create a Link from desired state to gap
• Create a Parameter and name it pct change factor
• Create a Link from pct change factor to action

Now that the model has been developed select the following items in the Library window and define them as follows:

• Model Settings
  • Time Step: 1 Weeks
  • Run Length: 10 Weeks
• action
  • Rate = [gap] - [Current State]
  • per 1 Weeks
• gap
  • Rate = [desired state] - [Current State]
• Data Display
  • Units of Time: Weeks
  • Uncheck pct change factor in Displayed Primitives list

Add a new Data Display, label it Data Table and configure it as follows:

• Tabular
• Units of Time: Weeks
• Displayed Primitives: check the following
  • Current State
  • action
  • desired state

The selection of Week as the unit for time is relatively arbitrary at this point. In any particular model it may be another value.

Using the View Sliders window check and define the following:

• Desired State: Minimum = 0; Maximum = 200; set at 100
• pct change factor: Minimum = 0; Maximum = 1; set at 0.1

Now save the model as Balancing Loop and you can run it.

Ok, now that you have everything defined click Run on the Value Sliders window and you should see the graph below in the Balancing Loop - Analysis 1 window with the tabular equivalent on the Data Table tab.

Notice how the Current State approaches the desired state more and more slowly as action declines.

Click Balancing Loop to run this model over in your web browser.

[edit] Effective Strategies

If you want the Balancing Loop to migrate the Current State to the desired state there are some specific things you might want to take into account.

• Ensure there is an explicit well understood and agreed upon definition of the desired state. If you don't know where you're trying to get to then any action will take you somewhere.
  
  
• Ensure there is an as objective as possible definition of the Current State. It is the relation between the desired state and the Current State that forms the basis for planning and subsequent action. If the planning is flawed there is a good chance the resultant action will be inappropriate to move the Current State to the desired state.
  
  
• Because action is driven by the size of the gap between desired state and Current State there is a natural tendency for the extent of action to decline as the Current State approaches the desired sate. This tendency accounts for the fact that as projects approach completion it seems to be more and more difficult to make progress toward completion. To overcome this tendency the motivation for action must come from somewhere other than the gap. In terms of project completion the focus might be to begin to think about completing this project so the organization can get on to the next one. The answer to the predicament lies outside the structure as presented.

[edit] Areas of Concern

The Balancing Loop is one of the simplest structures and seldom ever occurs in isolation from additional influences. Look at the structure of the Balancing Loop and think of some things that might happen to change the behavior of the Balancing Loop.

• Since you can never do just one thing, and the fact that the Current State is what it is for some reason, the action taken to change the Current State, or the change in the Current State itself, may produce side effects which in fact cause the Current State, in time, to return to its initial state, which implies a Fixes that Fail Systems Archetype.
  
  
• If the period of time over which it takes action to move the Current State to the desired state is relatively long there may be a willingness to settle for less than the initial desired state. In this instance the desired state is never reached because the desired state is lowered over time, which implies a Drifting Goals Systems Archetype.
  
  
• Pursuing the desired state may cause problems elsewhere. These problems may actually result in increasing the desired state making it more difficult to reach, which implies an Escalation Systems Archetype.
  
  
• The situation may be such that the action taken to achieve the desired state actually causes the Current State to overshoot the desired state. This would then require additional action to bring the Current State back toward the desired state, which implies a Balancing with Delay Systems Archetype.
  
  
• It is also possible that there is a delay such that the structure promotes an endless oscillation, which implies an Indecision Systems Archetype.

[edit] Examples

• Balancing Loop Examples

[edit] References

• Causal Loop and Stock & Flow Diagrams created with Vensim
• Simulation created with Simgua

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