What is an interrelationship diagram?
Complex problems rarely have a single cause; their causes influence each other. An interrelationship diagram makes these links visible. It places the issues in a circle, draws an arrow from each cause to its effect, and counts the arrows. Issues with the most arrows out are the key drivers: improve them and many other issues improve too. Issues with the most arrows in are the key outcomes: they show the problem, so they make good measures of success.
How to build an interrelationship diagram
- Agree the problem statement and gather 5 to 25 issues.
- Compare every pair: is there a cause-and-effect link, and which way is it stronger?
- Draw one arrow per related pair, from cause to effect.
- Count the arrows in and out of each issue.
- Identify the key drivers and key outcomes, and check them against data and experience.
Interrelationship diagram example
A team investigating batch record errors lists eight issues. Working through each pair, they find that "forms change often without notice" drives three other issues: classroom-only training that falls behind, forms with many free-text fields and time pressure at the end of the shift. It is the key driver. "The same errors repeat across shifts" receives four arrows: it is the key outcome to track. The conclusion surprises the team: the first lever is document control, not more training.
After the diagram
- Confirm the drivers with data, for example a stratification or scatter diagram.
- Plan how to tackle the key driver with a tree diagram.
- Use the key outcome as the measure in your PDCA or A3.
How to use this Interrelationship Diagram tool
- State the problem. Click the dark box and write the problem or issue being analysed.
- Add the issues. Click + in the centre to add each factor (5 to 25 work best), e.g. from an affinity or fishbone diagram.
- Decide the relationships. In the matrix, click each pair: → if the row drives the column, ← if the column drives the row, blank if unrelated.
- Read the drivers and outcomes. The diagram counts arrows in and out and highlights the key driver (green) and key outcome (amber).
- Check with the team. Discuss whether the drivers make sense and confirm them with data where possible.
- Export. Export the diagram and the counts to PDF, PNG or Excel.
Frequently asked questions
What is an interrelationship diagram?
An interrelationship diagram (or interrelationship digraph, or relations diagram) shows cause-and-effect relationships between several issues or factors. Each issue is a box; arrows go from cause to effect. Counting the arrows in and out of each box identifies the key drivers (most arrows out) and key outcomes (most arrows in).
How do you read an interrelationship diagram?
Issues with many outgoing arrows are drivers: root causes or levers that influence many other issues, so acting on them has the widest effect. Issues with many incoming arrows are outcomes: symptoms that are useful to measure but hard to change directly.
How do you decide the direction of an arrow?
For each pair of issues, ask "Is there a relationship? If so, which one drives the other more?" Draw only one arrow per pair, in the stronger direction. If neither clearly drives the other, leave them unlinked.
When should I use an interrelationship diagram?
When a problem has many interacting causes and the team needs to find where to start, often after an affinity diagram or fishbone diagram has produced the list of issues. It works best with 5 to 25 issues.
What is the difference between an interrelationship diagram and a fishbone diagram?
A fishbone diagram lists possible causes of one effect in categories, as a tree. An interrelationship diagram shows how the causes affect each other, which reveals the drivers among them. They are often used together: fishbone first, then interrelationship diagram on the main causes.
Is this one of the seven management and planning tools?
Yes. The seven management and planning tools are the affinity diagram, interrelationship diagram, tree diagram, matrix diagram, prioritization matrix, process decision program chart and arrow diagram. All seven are available free on this site.