When using a cause and effect diagram to find root causes, beware of clutter. Using a list instead of a diagram makes the cause and effect tool easier to use and allows more flexibility.
But whether you use the traditional diagram or a bullet list, put the same powerful concept to work.
First, find the root causes—then begin problem solving. If you solve a problem before you know what caused it, it is likely you have not really solved the problem. And, chances are, it will return.
A powerful tool for finding root causes is the cause and effect diagram, which Karou Ishikawa invented in the 1960s (see Online Figure 1). The cause and effect diagram is sometimes called an Ishikawa or fishbone diagram.
Without this tool’s discipline, we might stop before we find the root cause. By using the cause and effect tool, we continue to search all the major categories of causes, increasing the likelihood of finding the real root cause.
To create a cause and effect diagram, start with an arrow pointing to a box. Write the problem in the box. Draw arrows to the line from the major categories of causes. In this example, we used people, materials, methods, equipment, measurements and environment (see Online Figure 2).
Study the process to determine causes from each category. For equipment, lubrication, speed and setup are possible causes. For people, training, fatigue, skills and motivation might be important. For methods, possibilities include definition and sequence.
Measurements might include instruments and calibration. For environment, light, temperature, humidity and vibration could be appropriate.
During the initial search, use the brainstorming rule—withhold judgment—to make sure you don’t miss a cause that might prove to be the problem’s root cause. Evaluations should be done later.
As you develop diagrams, it becomes more difficult to record more causes. The clutter might result in good ideas being overlooked or not recorded at all.
Recently, in one of Conbraco’s Calibration College classes, I learned a better way to perform cause and effect searches. This method is easier to create and makes recording causes more flexible.
Conbraco employee Jenny Stavrakas knew about cause and effect diagrams but was bothered by their clutter. So, she developed a format to reduce clutter while keeping the tool’s simplicity and power.
Stavrakas’ technique is to create lists on a whiteboard, flip chart, sheets of paper taped on walls or on a computer. She nicknamed them cause and effect bullet lists. These lists work well when you can project them on a screen so everyone developing them can see causes as they are recorded.
To work with your team in developing a list, first record the problem. Start with one category, and list all the causes that might be creating the problem. Get inputs from appropriate people, such as operators, technical experts and maintenance workers. Continue through the other categories. Stopping too soon might result in missing the real root cause.
Then, identify the most likely root causes, and test for a cause and effect relationship (consider using a scatter diagram). Correct the causes creating the problem, and then change the process, confirm the new results and establish controls to make sure the new process is used.
For example, let’s use some of the content from the fishbone diagram example in Online Figure 2:
Try a cause and effect bullet list to experience its simplicity and flexibility. Whether using a diagram or a list, finding the root causes before beginning problem solving is key.