Vol. 5, No. 7

Dr. Noah Tahl is totally confused about these two useful quality tools. A cause-and-effect diagram is a picture of various system elements that may contribute to a problem or outcome. Thus, it is used to get to root causes. Pareto diagrams, however, sort data by frequency of occurrence, but do not pretend to identify causal relationships.

The cause-and-effect diagram was developed in 1943 by Professor Kaoru Ishikawa, President of the Musashi Institute of Technology in Tokyo. It is sometimes called an Ishikawa diagram or a fishbone diagram because of its resemblance to the skeleton of a fish.

Used to identify possibly variables influencing a problem, outcome, or effect, he graphic nature of the diagram allows groups to organize large amounts of information about a problem and pinpoint possible causes. It also encourages investigation of causes at many levels, improving odds that root or basic causes will be identified. 

In health care settings, the cause-and-effect diagram can be used, for example, to identify the variables influencing carpal tunnel syndrome outcomes or high-risk pregnancy outcomes. The cause-and-effect diagram is also useful in identifying variables influencing the outcome or effect of support processes such as medication delivery, billing, purchasing, or scheduling, and can  identify variables involved in general problems such as absenteeism, turnover, or wait time.

The cause-and-effect diagram is used to find special or common causes of variation and to analyze causes. It can be used to solve unexpected or everyday problems of the system. Although the diagram looks simple to make, it is not easy to do well. Kume, a Japanese quality professional, has said, “It may safely be said that those who succeed in problem solving in quality control are those who succeed in making a useful cause-and-effect diagram.”  

To learn more about cause-and-effect diagrams or Pareto charts, refer to Practical Tools for Continuous Improvement, a two-volume collection of statistical, problem-solving, and planning tools.