Ishikawa diagram

The method finds the causes of a problem when several factors add up to it.

It was introduced by Kaoru Ishikawa, professor at the University of Tokyo.

When to use it

1. When you know the problem comes from several causes laid on top of one another, and you want to see them laid out before acting against them.
2. When 5 Why has not given you the answer you hoped for.

When not to use it

1. When you still do not understand what exactly happened; see 5W+H.
2. When you have not ruled out a single cause — in that case start with 5 Why.