Fishbone analysis / Cause-effect diagram/ Ishikawa diagram

The goal of a fishbone chart is to list all possible causes that could potentially lead to a particular defect.

Typically, fishbone analysis is done by brainstorming with personnel that have knowledge of the process or customers concerns. A brainstorming team may include process engineers, equipment operators, manufacturing engineers, quality engineers, maintenance team etc.

Even causes that have a low probability of occurrence may be noted on the fishbone chart. After completing the fishbone chart, the next step is to rule out the listed root-causes until the actual root-cause of the defect is found.

Pareto chart

It is simply a bar chart of defect types or defect causes listed in the descending order of occurrences. As a thumb rule, 80% of the defects/scrap is caused by 20% of the causes. Thus, a pareto chart is used to narrow the focus of improvement on the root-causes leading to most of the defects.

Fault-tree analysis (FTA)

A fault-tree chart is similar to a fishbone-chart except that the fault-tree is a structured. Unlike fishbone analysis, in FTA the potential root-causes are organized using a MECE approach.

The MECE principle is a grouping principle for separating a set of items into subsets (categories) that are mutually exclusive (ME) and collectively exhaustive (CE). Mutually Exclusive (ME) means items can only fit into one category at a time i.e. there are no overlaps among categories. Collectively Exhaustive (CE) means that all the categories taken together represent the entire scenario i.e. there are no gaps between the categories.