Guidelines On Causal Loops

Causal Loops Influence diagrams

Dennis T. Beng Hui, De La Salle University-Manila

What are causal loops? „ „ „ „

Most commonly used tool in the early stages of system conceptualization. Also called influence diagrams, or directed graphs. A diagram that shows causal links among actions, information, and consequences. A positive link increases the value of the link, while a negative value decreases the value of the link. Dennis T. Beng Hui, De La Salle University-Manila

Guidelines for Causal Loop Diagrams: ƒ Refer to the variables in the loop as quantities that can rise or fall, grow or decline, up or down. There is no need to know how they can be quantified. ƒ Use nouns or noun phrases and not verbs. The actions are represented in the arrows. ƒ Be sure that it is clear what it means to say, “ a variable increases (decreases)….” Dennis T. Beng Hui, De La Salle University-Manila

Guidelines for Causal Loop Diagrams: „ „ „ „

Do not use causal links to mean “ and then …” Identify the units of the variables as much as possible. If necessary, invent it. Phrase the variables positively. If a link needs explanation, disaggregate it and make it a series of links.

Dennis T. Beng Hui, De La Salle University-Manila

Guidelines for Causal Loop Diagrams: „ Do

not interpret open loops as feedback loops. „ The sign indicates whether the succeeding variables increase (positive) or decrease (negative), when the previous variable increases. „ Keep diagrams simple to start with. „ Watch out for unintended effects. Dennis T. Beng Hui, De La Salle University-Manila

Guidelines for Causal Loop Diagrams: „ Distinguish

carefully between actual values and perceived values. „ When using a variable such as “actual values”, look for corresponding “desired values”. „ Be clear about the purpose of the model. Is it top level, strategic, or a detailed tactical problem? Dennis T. Beng Hui, De La Salle University-Manila

Types of Loops „ Negative

feedback loop – if it contains an odd number of negative causal links „ Positive feedback loop – if contains an even number of negative causal links

Dennis T. Beng Hui, De La Salle University-Manila

Value of Influence Diagrams „ Simplicity „ Tool

for communication „ Does not require intimate knowledge of on the simulation techniques of SD

Dennis T. Beng Hui, De La Salle University-Manila

What is a good diagram? „ Have

the purpose and target audience of the diagram been carefully chosen? „ Are the factors chosen consistent with the purpose? „ The objective of SD is policy analysis, so are the policies clearly shown in the diagram? Dennis T. Beng Hui, De La Salle University-Manila

What is a good diagram? „

„ „

SD aims to produce policies which are robust against a range of circumstances, so are the exogenous factors which might present the system with setbacks or opportunities clearly identified? Are the variables capable of being easily explained to the target audience? Are these variables, in principle, capable of being measured? Can they vary over time? Dennis T. Beng Hui, De La Salle University-Manila

What is a good diagram? „ Does

it capture the most significant insights? Was it drawn after careful analysis? „ Can the diagram be drawn on level lower or higher without losing conceptual consistency? „ Is the diagram too complicated that it may fail to communicate? Dennis T. Beng Hui, De La Salle University-Manila

What is a good diagram? „ Is

the diagram neat and tidy with minimum number of lines crossing? „ Can feedback loops be clearly seen? „ Do I understand the diagram myself before I try to explain it to someone else or write about it?

Dennis T. Beng Hui, De La Salle University-Manila

Notations for Causal loop Diagrams Physical Flow Information Transmission Control Action Behavior of Nature Parameter Flow

Parameter

D1

Delay in Physical Flow

FORCE Forces outside the system where the manager has no control

FORCE Dennis T. Beng Hui, De La Salle University-Manila

Reading a Causal Loop „ Place

the signs (+ or -) at the head or point of the arrow. Influencing Variable

Influenced Variable

Positive Links

Negative Links

Dennis T. Beng Hui, De La Salle University-Manila