Science, Maths & Technology

# Influence diagrams

Updated Monday, 21 June 2021
Ever wondered what an influence diagram is or how to draw one? These video tutorials explain...

## Diagram guidelines

### Purpose

An influence diagram is a straightforward development from a systems map that explores the influences between the components that you have included on the map. It therefore represents how the components both of the system and its environment interact, and shows the important relationships that exist among them. It presents an overview of areas of activity, or organisational and other groupings, and their main interrelationships. It is used either to explore those interrelationships, perhaps leading to a regrouping and redefinition of the system and its components, or to express a broad view of how things are in the territory you are considering. Influence diagrams can be developed from a systems map by adding arrows and can be used as the starting point for a multiple cause diagram. However, note the difference between the components that are the nodes in the influence diagram and the events or states that are the nodes in the multiple cause diagram.

### Elements

• A title giving the purpose of your diagram.
• A system boundary with the system purpose displayed on it.
• System components described in words or short phrases within the boundary.
• Environmental components described in words or short phrases usually ringed outside the boundary.
• Assorted arrows representing the influences between components.
• Possibly words or short phrases labelling arrows.
• A key for arrows where colour or thickness is used to display strength of influence.

### Conventions

• A purpose defining the system of interest is important – ‘A system to …’
• Words are used to name each component of the system and the environment you include.
• These sets may overlap only if some components (which need not be depicted) are seen as common to both in the early stages of exploring your system of interest.
• An arrow joining components shows that one can or does influence the other, the direction of the arrow showing the direction of the influence.
• A double-headed arrow should never be used to denote a two-way influence unless the influence is identical – two separate arrows should be used.
• Words label components, and they may also label arrows if the nature of the influence is not obvious from the context. Alternatively, dotted or bold lines can represent different influence as long as a key is given.
• Arrows denote capacity to influence, not a sequence in time.

### Guidelines

• Avoid using arrows from features in the environment to the system boundary. Arrows from environmental components should terminate at a specific system component where possible. Arrows to the system boundary carry information only if they distinguish different types of influence.
• It is possible to distinguish different types of influence (e.g. influence via finance, information, supply of materials). Do so only if such distinctions are important and not self-evident, by the use of different lines (colour, dashing) to show this, and a key to explain them.
• Resist the temptation to overload the diagram with information. It may be helpful to you to put down all influences you can think of at first, but for communication to others, select the significant ones.
• Resist the temptation to use double-headed arrows. Use them only when the influence is truly reciprocal and of the same type. If you are not careful, the use of double-headed arrows can obscure important differences in the types of influence and their magnitude, which is seldom, if ever, equal. Use two arrows pointing in opposite directions instead.
• Space and relative distance can also be used to suggest things about the nature of the relationships shown (e.g. an important but remote relationship).