Influence Diagram

What is an influence diagram? Closely related to decision trees and often used in conjunction, influence diagrams are a summary of information contained in a decision tree. They involve 4 variable types for notation: a decision (a rectangle), chance (an oval), objective (a hexagon), and function (a rounded rectangle). Influence diagrams also use solid lines to denote influence. Their appearance is very similar to a flowchart.

Influence diagram

What's the Difference Between Decision Trees and Influence Diagrams?

Influence diagrams show the dependencies among variables. This is an important distinction between influence diagrams and decision trees. Decision trees offer much more detail about each possible decision.

Symbols Used in an Influence Diagram

An influence diagram involves 4 variable types for notation: a decision (a rectangle), chance (an oval), objective (a hexagon), and function (a rounded rectangle).

Influence diagram symbols

Typical Uses of Influence Diagrams

If a decision tree is very complex and needs to either be explained to someone or presented, an Influence Diagram is very helpful as it will give an higher level explanation of what was discovered using the decision tree.

How to Create an Influence Diagram

There are many different ways to create an influence diagram. They can be created using pen and paper, white boarded, or, more efficiently created by diagramming software.

Here are some best practices in creating an influence diagram:

  • Start your tree. Draw a rectangle near the top-left corner of the page. This will be the first 'node' or shape. In this rectangle write the first question or a criterion that leads to a decision.
  • Add to the process. Referencing the decision tree, add more shapes to the page as needed, labeling each. A series of decisions, functions, and chances should lead to an objective.
  • Add connectors. Use a combination of straight or angled lines between all related boxes with arrowheads indicating the flow of influence. Each box should be connected to at least one line.