Finding the cause of problems

Control charts (and other collected data) may indicate problems with a system. For example,

However, after detection of a problem, its cause must be identified in order to rectify it. This is usually a non-trivial exercise and the following tools often help.

Brainstorming

Continuous quality improvement is usually performed by a team, and a good way to get ideas is with a brainstorming session. In this, all team members contribute short phrases that are written on either a large sheet of paper or individual scraps of paper (post-it notes are good). The points should be written down without discussion or editing, and all team members should be encouraged to contribute.

Once these ideas have been written down, they must be structured or grouped in some way.

Cause-and-effect diagrams

After possible causes for a problem have been contributed in a brainstorming session, they can be structured in a cause-and-effect diagram. In this,

Because of the shape of this diagram, it is often called a fishbone diagram.

This structuring of possible causes helps to focus attention on the most likely causes and on ones that may be altered in the 'Do' step of the Plan-Do-Check-Act cycle.

Failure rates in a university

University management has observed that failure rates in first-year papers have increased in the past ten years and want to understand the problem before adopting any new policies that may improve student performance.

The cause-and-effect diagram below shows potential causes for the problem that were suggested in a brainstorming session.

Drag the slider to see how the cause-and-effect diagram was constructed.