The Cause and Effect (or Fishbone) human reliability method, is used to identify the main causes of a given human error. The diagram, which resembles the skeleton of a fish, includes the fish head, which denotes the human error, and the fish bones, which denote all possible causes of the error. The causes are connected through the central line of the diagram, referred to as the fish spine. The steps followed to develop a cause and effect diagram, are: 1) Establish problem statement 2) Brainstorm to identify all possible causes for the human error under consideration 3) Develop appropriate main cause classifications by stratifying into natural groupings and process steps 4) Show the cause classifications diagrammatically as fish bones joined through a fish spine. 5) Complete the diagram by joining the end of the fish spine to the fish head, which shows the human error under consideration 6) Refine cause classifications as considered appropriate by asking questions such as Why does this condition exist? and What causes this? See also: Ishikawa analysis (fishbone) method in IEC 31010:2019, B.3.3

Example problem: After a careful investigation, it was established that there are four main causes I, II, III and IV for a railway signalman to commit an error. In turn, there are two sub-causes a and b associated with Cause I, three c, d and e with Cause II, two f and g with Cause III, and three h, i and j with Cause IV. Develop a cause and effect diagram for this example problem.