Cause and Effect Diagram
Use when asked to run a root-cause analysis session using a fishbone/Ishikawa-style diagram — the 6M cause categories (Manpower, Methods, Machines, Materials, Measurements, Mother Nature) — the same technique also called fishbone-diagram or ishikawa-diagram under alternate names.
A cause-and-effect diagram — also called an Ishikawa diagram (after its developer, quality-control expert Kaoru Ishikawa) or a fishbone diagram (after its shape) — is a visual tool for analyzing and solving problems by systematically identifying their possible causes. See Fishbone Diagram and Ishikawa Diagram for the identical technique under its other common names — all three names refer to the same tool.
Shape and structure
The diagram is shaped like a fish skeleton: the problem statement or effect sits at the head, and potential causes branch out along the spine as "bones" — each major bone representing a cause category, with specific candidate causes listed as smaller branches off each one.
The 6M cause categories
A common set of categories used to organize brainstormed causes (originating in manufacturing, but adaptable to other domains):
- Manpower — people-related causes.
- Methods — process-related causes.
- Machines — equipment-related causes.
- Materials — input-related causes.
- Measurements — data-related causes.
- Mother Nature — environmental conditions.
Not every category applies to every problem (a software-specific version often adapts these — e.g. swapping "Machines" for "Tools/Infrastructure") — the categories are a starting checklist for prompting broad brainstorming, not a rigid requirement to fill in every branch.
The process
Brainstorm possible causes of the problem (see Brainstorming for running that step well) and organize them into the cause categories, typically in a group setting with people who have real knowledge and experience relevant to the problem. Once causes are identified, analyze and prioritize them, then develop and implement potential solutions targeting the most likely or highest-impact root causes.
Why it's useful
Built on the premise that a problem usually has multiple contributing factors, not one single cause — addressing only the first plausible cause found risks missing the actual root cause(s). It's also a strong collaboration tool: structuring the brainstorm by category naturally brings together different areas of expertise and perspectives that a free-form discussion might not surface as systematically.
Common pitfalls
- Stopping at the first plausible cause — the whole premise of the technique is that problems are usually multi-causal; treating one identified branch as "the" answer defeats the method's purpose.
- Forcing every category to have an entry — not every cause category applies to every problem; padding a category with a weak, unlikely cause just to fill it in dilutes the diagram's usefulness.
- Skipping prioritization after brainstorming — a fishbone diagram full of unranked candidate causes doesn't by itself tell you which to actually address first; a follow-up prioritization step (by likelihood and impact) is necessary to turn the diagram into action.
- Running it solo instead of with a knowledgeable group — the technique's collaborative, multi-perspective brainstorming is a significant part of its value; one person's cause list is more likely to miss whole categories of contributing factor.
Learn more
- Fishbone Diagram, Ishikawa Diagram — the same technique under its other common names.
- Brainstorming for running the cause-generation step well.
- DMAIC for the broader Six Sigma methodology this technique is commonly used within (typically during the Analyze stage).