Finding the Root Cause - Which technique is better?

[TShepherd]

Good morning,

Sorry I haven't had a chance to respond sooner in this thread and maybe this is too late.

I read all of the responses and feel there was some really good information shared.

Here is my

Bottom line: Concerning the Fish Bone and the 3L5W (three legged five why)

My experience has taught me that the fish bone in conjunction with the 3L5W is a fairly good combination and yes there are many other combinations that also work.

Identifying the possible contributers:

The fishbone may be used to ensure that as many of the possible contributers to the problem are captured as possible.

Set your priorities for investigation based on the outcome of the fishbone.

Test your priorities based on the fishbone outcome with any of a hundred quality tools that may be appropriate.

Test your analysis with the 3L5W

The 3L5Y is a great concept to test your engineering thought process - to see if it makes sense.

Validate the outcomes of your investigation through any known means as you can. (can you turn it on and off?) - and I believe everyone understands that there can be more than 3 legs and more than 5 whys or less tha 5 whys, the 3L5Y is merely a starting point to test your your thinking - that is what the customer normally wants - to see if your response makes sense.

I have attached a couple of 3L5Y templates I have used in the past and the fishbone templates from an earlier post look really good.

Best Regards and good luck,

Tom

 

[TShepherd]

I see that a few war stories for problem solving have popped up. here is a short one.

I worked at a plant for General motors that during WWII built machine guns - if you have ever seen the guy aiming a machine gun that was setting on a Tri-pod - that was the gun. (p.s. - they also built a 1 shot 45 caliber that was dropped behind enemy lines for the resistance fighters)

After the war the machines that built the guns was transformed over to power steering gears.

One of those machines were several Gisholt Cridan Lathes that were used to machine a spiral grove on a shaft where ball bearings ride.

We used these lathes successfully for more than forty years to machine worm gears for every gear that went into a car or trucks.

After my retirement in 98, I was called back and asked to travel to Mississippi as they were changing the Lathes from manual lathes to CNC controlled and couldn't make a good part to save themselves.

I agreed and arrived at the appointed date and time.

I was led out to the floor and asked to go through the set-up and produce a good part.

I was surrounded by young engineers that didn't really want me there (I could tell)

After setting the machine up and running a few parts - I took one to the gage (Dial indicator) and and ended up with a darn near perfect part.

They told me I was putting the part in the gage backwards - after a lively discussion they sheepishly agreed that the correct way to gage the part was now known.

Moral to the story: check your gages.

 

[dwayne_dhey]

Re: It's simply not that simple

Then, how could we determine a symptom from the root cause?Is there a definition of root cause provided by ISO?

 

[JaneB]

Re: It's simply not that simple

Then, how could we determine a symptom from the root cause?Is there a definition of root cause provided by ISO?

To my knowledge, there's no official one (it's not provided in ISO 9000 Fundamentals and vocabulary) but it is a widely used term in quality management, not just ISO.

The question you ask is the key point. I'm guessing you mean 'how can we distinguish what's a symptom from a root cause'? (By the way, I deliberately say a root cause rather than the root cause, because there's not necessarily a single cause. Sometimes indeed, there's a combination of factors.)

Some of the techniques used toThe '5 Why's' is one good method for working out what is a symptom and what is a cause. There's plenty of info on root cause analysis on the web if you search, and using 5 Whys (broken link removed)and also here.

 

[dwayne_dhey]

Thanks Ms. Jane, I deeply appreciate your reply and I do hope to continue this knowledge sharing activity. I am still searching for a definition but unfortunately, none so far. It will be used in the preparation of a module on risk assessment since one of the components of a risk description is cause. To help trainees understand better, a definition for cause-root cause- will be presented including samples in the public sector. Again, thank you very much.

 

[ssz102]

i think use 5M1E method to be better analysis these problem

 

[Bev D]

Re: It's simply not that simple

Then, how could we determine a symptom from the root cause?Is there a definition of root cause provided by ISO?

First, I don't use the term 'symptom'. the medical analogy isn't all that helpful IMHO. I prefer to use the term 'effect'.

Problems are the result of a sequence of cause and effect. The first cause has an effect, that first effect is the casue of the second effect, etc.

My operational definition of 'root cause' is that factor (or interacting set of factors) that is actionable and that action will prevent the Problem from ocurring in the future (due to that factor). Often we find intermediate causes that enable us to rework or repair something when it experiences the Problem but this is containment. so the definition of 'root cause' is somewhat subjective; certainly not a law of physics.

to tell you the truth, I don't even like the phrase 'root cause'. I much prefer the phrase 'causal mechanism' as it encompasses interacting factors, independent factors and conditions for failure.

 

[JaneB]

Thanks Ms. Jane, I deeply appreciate your reply and I do hope to continue this knowledge sharing activity. I am still searching for a definition but unfortunately, none so far. It will be used in the preparation of a module on risk assessment since one of the components of a risk description is cause. To help trainees understand better, a definition for cause-root cause- will be presented including samples in the public sector. Again, thank you very much.

May I suggest that in hunting for a definition, you are hunting for something that actually doesn't exist? And that a more fruitful search might be to look for the characteristics (or attributes) of a root cause, which would give helpful guidelines for the use you want to put it to.

For example, I think this from wikipedia offers some sage advice.

One of the difficulties encountered in root cause analysis is knowing when you have found a bona fide root cause. A checklist of the characteristics of a root cause can help the analyst separate pseudo root causes from real ones.

A 2010 paper on Change Resistance as the Crux of the Environmental Sustainability Problem used root cause analysis to find two main root causes of the sustainability problem. The paper presented three characteristics of a root cause:
"A root cause is a portion of a system’s structure that 'best' helps to explain why the system’s behavior produces a problem’s symptoms. Difficult problems usually have multiple root causes. These are found by asking a succession of 'Why is this happening?' Kaizen-like questions until the root causes are found. "How do you know when to stop?

A root cause has three identifying characteristics (compare to Rooney and Heuvel, 2004, who list 4 characteristics):
1. It is clearly a (or the) major cause of the symptoms.
2. It has no worthwhile deeper cause. This allows you to stop asking why at some appropriate point in root cause analysis. Otherwise you may find your-self digging to the other side of the planet.
3. It can be resolved.
Sometimes it’s useful to emphasize unchangeable root causes in your model for greater understanding and to avoid trying to resolve them without realizing it. These have only the first two characteristics.
This definition allows numerous unproductive or pseudo root causes to be quickly eliminated.

The important thing is to not stop at intermediate causes. These are plausible and easily found. Working on resolving what are in fact intermediate causes looks productive and feels productive. Intermediate cause solutions, more accurately called symptomatic solutions, may even work for awhile. But until the true root causes are resolved, powerful social agents will invariably find a way to delay, circumvent, block, weaken, or even rollback these solutions, because intermediate causes are symptoms of deeper causes. One must strike at the root." While the paper dealt with a social problem, the three characteristics apply to problems of any kind.

 

[Deep Krothapalli]

As Jane has pointed out- the most important aspect of finding root cause is to drill down, and not settle at the top level plausible causes.

Prior to going to fish bone/cause-effect method, I found - IS-IS Not helpful in defining what sort of additional information is needed. In fact, there were instances that I didn't even use fish bone, and was able to get the root cause from IS-IS NOT diagram. It really depends on what stage you are at in "Define" phase of the project.

Deep

 

[buffalo_hua]

Fishbone is used for analysing any possible causes, if you guys have found many causes by brainstorming, then pls. use 5-why to analyse / determine the ROOT causes. Hope it is helpful to you.