Casual loop diagram

• The Essay topic: Casual loop diagram
• Class:4IT496 Simulation of Systems (WS 2014/2015)
• Author: Martina Nováková

Introduction

Everything is connected to everything else. It doesn´t matter if it is nature or human environment, there is a large and complex web of interactions. But sometimes we need only sections of these connections, and so we have to isolate issues which we would like to describe and observe. There are different word and arrow diagrams, e.g. causal-loop diagrams, cognitive maps or fishbone diagrams. They are widespread in system dynamics. This chapter is concentrated on issue of causal loop diagrams. (Haraldsson, 2000)

Description of causal loop diagrams

Causal loop diagrams (CLDs) are a very simple but powerful way of visualizing important parts of the system and how they interrelate. It is a great tool for dealing with complex problems and the striking component of system dynamics.

Causal loop diagrams are useful for displaying the behaviour of cause and effect from system standpoint. they show the interrelation between causes and their effects. They are quite popular because it is easy to start drawing these diagrams. All you need to draw CLDs is pencil and paper or a whiteboard. You can use software for drawing this type of diagram too. These possibilities will be introduced later.

As stated above there are other tools which are used for modelling of system dynamics. One of them which could seem the same as Casual loop diagram is a Fishbone diagram (or we can call it Cause and effect diagram). But this diagram is different because he can induce categories of causes that impact a problem. Although CLDs focuses on causation too, there are differences because CLDs are more general and more expressive than fishbone. (Osgood, 2004). After finishing this diagram there is diagram of the negative and positive reinforcements.

The main principle of the Causal loop diagram is quite simple. Parts of a system are visualized using textual identifies. The connections between the parts are shown using arrows pointing in the direction of influence. Creating the causal loop diagram with given system is actually quite simple. we start with the parts we already know and keep asking what influences this part has until we reach parts that are at the systems boundary. There are all parts that do not change. Then you go in the other direction and keep asking which other parts of the system influence this part If that part is already there you connect it otherwise you create a new part.

Symbols of CLDs

There will be explained main symbols of causal diagram loops and procedure of its creation. If we want to put system in practise, we have to follow some rules. There are several causal loop concepts. (Haraldsson, 2000)

The arrow is used to show causation. The item at the tail of the arrow influences the item at the head of the arrow.

The + sign near the arrowhead signifies that the item at the tail of the arrow and the item at the head of the arrow change in the same direction. If the tail increases, the head increases; if the tail decreases, the head decreases.

The – sign near the arrowhead indicates that the item at the tail of the arrow changes in the opposite direction. If the tail increases, the head decreases; if the tail decreases, the head increases.

The symbol B, which is in the middle of a loop, signifies that the loop moves away from equilibrium point. This loop continuous going in the same direct. This is called a positive feedback loop.

The symbol R, which is in the middle of a loop, signifies changing direction of the loop. It means that the system move toward equilibrium. This is called a negative feedback loop.

CLDs in practise and their problems

Problem of CLDs

For many types of examples it is clearer to use a hybrid diagram which contains stock-flow chain. But this could be harder for visual language. There are many problems with notation too. There is not uniform labelling. Sometimes it is used an “s” (means “same”) and “o” (means “opposite”) instead of the + and -. This problem is explained by George Richardson in his paper “Problems with casual loop diagrams” and his conclusion is that it is not good to use “s” and “o” because it is less confusing. (Richardson, 1986) .