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An Ishikawa (or fishbone) diagram is a visualization tool to diagram and explore cause and effect relationships. It is commonly used for root cause analysis when a problem has been identified by observation, customer surveys, or statistical process control. It is also used at the fuzzy front end of experimental design to explore all of the factors that might contribute to changes in an effect or response variable. This article explains how to make one with the Six Sigma package in R.
Background
An Ishikawa diagram connects causal links in major categories with an outcome, or effect (see Figure 1). The process, which can be performed by one person alone but is particularly effective when performed in groups, goes like this:
1. Establish a goal: Identify the desired effect or, alternatively, describe the problem whose root cause one wants to identify.
2. Establish the structure: Choose the appropriate design pattern for the fishbones.
3. Brainstorm: For each fishbone that is identified, brainstorm as many possible factors that might cause a change in the effect. Write those possible causes along the bone.
4. Down select and prioritize: Revisit the potential causes, and reduce them to the...