Fish Bones, Cause and Effect

The Ishikawa Diagram has been an old standby in Quality Management and other applications of structured problem solving for quite awhile.  You may know this technique by another name: the fishbone diagram, the cause and effect diagram, 6M’s, etc.

Let’s use a children’s story, the Pied Piper of Hamlin, to illustrate the use of this technique.  As the story goes, the good people of Hamlin were plagued with rats.  The rats were eating all the grain and food in town.  The angry people went to the Mayor, insisting that the Mayor do something about this horrible problem.  The Mayor had read the Global Quality Blog and remembered a problem solving technique, the Fishbone diagram.  The Mayor drew a horizontal line, like this:


The Mayor used the “Measurement, Materials, Methods, Manpower, Machines, and Mother Nature” categories (6M’s).  The Mayor also used ASQ.org’s reference page for the Cause and Effect diagram.


Luckily, the Mayor wasn’t left to do this alone.  The Townspeople were more than glad to help out.  They were tired of chasing rats out of their houses and finding rats in the grain bins.  So, the Mayor asked the Townspeople- “How many rats have you seen?”

The Townspeople answered, “Lots and lots of rats!”

The Mayor, replied- “Ok, more than 10?”

“Yes, hundreds of thousands of rats!”, exclaimed the Townspeople.

The Mayor added this to “Measurement” on the fishbone diagram.

The Townspeople and Mayor continued adding ideas for why there may be rats in Hamlin.  “There seem to be more rats in winter than in summer, but I never see a rat in town before harvest time.” “I wonder why there’d be more rats in winter?”

“I see them in the fields in summer and they’re not much trouble. Günter (my hound) scares them off pretty easily.”

“I’ve seen them run across the ropes to the pier from the river boats!”

“I saw one chew right through the floor boards of the grain silo.”

And on it went.  They added to each category of the fishbone diagram, and it looked like this:


“If the rats come for the grain, can’t we just get rid of the grain?”

The Miller is not too happy about this, “If farmers don’t bring grain to Hamlin, I won’t be able to make flour”.

“What! No flour?” said the Baker.  “If there isn’t any flour, then there’ll be no bread!”

“No bread! Then we’ll be as hungry as the rats!” said the Townspeople.

“Hold on, now” said the Mayor, “Let’s look at our drawing.”

They all look at the drawing and start talking about what may be bringing rats to Hamlin.  They circle the most important causes.


“Rats are always on the ships and barges, but the ships carry the most grain.”

“Well, there were holes in most of the grain sacks.  I saw a bunch of spilled grain on the ground.”

“Ok, if we all mend the sacks and baskets then maybe there won’t be spilled grain on the ground.”

And that’s what they did.  They also fixed the floor boards in the grain silos.

The End

Learn More:

-What may have really happened in Hamlin-

-Rat plagues of the Middle Ages-

-Support Wikipedia-

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