Cause and Effect Analysis

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Hello all, today we will explain What is cause and effect analysis? How it’s performed? The cause and effect analysis structure also known as fishbone diagram.

The learning objective of this article is,

  • What is cause and effect diagram?
  • Types of cause categories in the study.
  • How to create a cause and effect diagram (Fishbone diagram)?
  • How to brainstorm the study to perform cause and effect analysis?

Also, the learning objective is to understand the objective of cause and effect analysis in the analyze phase of Six sigma.

The Cause and effect diagram is also known as Ishikawa’s fishbone diagram. As its named after the Japanese professor Kaoru Ishikawa who first used it to investigate the causes of quality problems. And this is a method then that helps a team to think together on paper, help them to post it on notes, help them to discuss the way of thinking.

The method consists of systematically identifying all the sources, that may contribute to the problems under investigation. It’s generally done in a brainstorming session with a team of people who are knowledgeable in the problem area.

The cause and effect diagram not only help in finding of the causes but also help as a means of recording the entire problem-solving process that the team is using.

Let’s discussed the Cause & Effect diagram (Ishikawa’s fishbone diagram). So, according to uniform format, the causes should be investigated / Found and recorded under several major categories shown as major stems in the diagram.

Types of cause categories in the study

The stems which are used to categorize the causes are as shown in diagram are.

  • Man (Manpower)
  • Machine
  • Material
  • Method
  • Measurement
  • Environment

So, for example the

Machine:

this means the equipment that you’re using, computers that you’re using, anything that’s required for this particular process. This stem means you have to identify the causes related to machine and write here in this category.

Materials:

then consists of raw materials, materials that are to be used for the equipment of that process step.

Measurements:

This are data generated for the process that are used to evaluate its quality at that point. It consists of measurement system use to validate the process quality.

Methods and procedures:

These are how the process steps are performed, what is the set of operating procedures, the standard operating procedure SOP that is then documented and used.

Manpower:

Operators or anyone involved in that process. The causes related to operator / inspector which is involve in the process is categorize in this stems.

Environment:

Here we’re talking not only about the environment but also the organizational structure, the logistics, the conditions and often you see for example management included in these in this list. Management policies, higher level decision rules, things that are maybe a little outside of the control of the process but that definitely affect the process.

So, the cause & effect diagram is here, it’s a communication tool. And you just put the causes in the diagram, such as at the start there is a problem / failure mention in diagram, back of that the fishbone structure to represent the causes which is leads to the problem/ failure. Then what could be possible causes due to machine, which creates the identified problems in the process, what could be causes due to material, etc. Could there be something with operator, in the shift. Like that find out the causes related to man, machine, material, method, measurement & environment as mention in Fishbone diagram.

  • The 8 P’s Use in service industry
    • People
    • Process
    • Policies
    • Procedures
    • Price
    • Promotion
    • Place / Plant
    • Product
  • The 4 S’s use in service industry
    • Surrounding
    • Supplier
    • System’s
    • Skill’s

How to create a cause and effect diagram (Fishbone diagram)?

Let’s investigate the example problem related to Damage problem, it’s a very physical result of this brainstorming session. when you’re investigating a problem related to a service then maybe you’d have to modify this format slightly but in general you want to try and keep the main structure similar.

We had a problem here relating to the failure of Damage (Shown in Fig.), after investigated / brainstorm by a team in assembly shop. So, the team sat together and just talked to all the people involved in the process, looked at the process and here’s the example of their fishbone diagram. Now, maybe here we don’t need to go through everything that you can see. All of these resulting then in a damage failure. So you can see how creative this can be and it doesn’t have to be perfect but you get all the ideas into the diagram.

After creating the Cause & effect diagram, we have the possible causes to generate the damage failure. Now the team would vote to select the most probable causes from possible causes. So normally everyone votes to pick causes that need to be investigated further through experimentation and analysis technique.

Now in these causes all are not a valid causes to create damage problem, so we are going to take vote from each team member again, that which cause leads more effect on creating damage or not. Then after the vote we have the very few probable causes which may crate the damage problem. Now we must go for further investigation on that probable causes using the experimental and analysis techniques (Cause validation tools) such as cause validation table, Why-why analysis etc. After this process finally we found the Root cause of the damage problem.

How to brainstorm the study to perform cause and effect analysis?

Brainstorming means using the brains of members of a team, discussing with them, working with them, you know in a very free way to find a list of all the causes that contribute to a problem on hand and possible ways of solving it. And generally, there is a certain set of conventions usually adopted in this. Sessions to maximize the amount of information generated.

  • You generally have a facilitator, someone who’s not part of the tea. They help in the sessions acting as a moderator;
  • Make sure that everyone has a chance to talk, not having any real biases for one problem cause or problem solution. And all the ideas are recorded. No idea should be rejected. at least at the initial states of the idea generation.
  • And a facilitator will then go around the table making sure everyone has a chance to discuss and at the end of the brainstorming session you then have the ideas/causes in the list. So they’re reviewed based on consensus so that you end up avoiding any really unfeasible solutions.
  • Now then you have a resulting diagram which we presented to the team for voting, to choose from them the top cause for further investigation.

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