Constructing Cause-and-effect Diagrams

Have you ever had a quality problem that couldn't be quantified through the use of statistics? The relationship between a problem's effect and its cause is sometimes obscure. To solve the problem, you may need to examine the entire process, identifying all the potential problem sources before you can determine the root cause. When visually displayed, this problem-identification process is called cause-and-effect diagramming.

Cause-and-effect diagrams are also known as "wishbone" or "fish" diagrams because of their shape. A cause-and-effect diagram has a central "back bone" with "ribs" branching off. The process used to create the diagram is known as flowcharting.

Cause-and-effect analysis is frequently completed by a team since specialists in many areas or departments may be required to provide input into their part of the process. During a project meeting or conference, the project team will construct the diagram, starting with the problem and working backward to the beginning of the project or process.

In cause-and-effect diagramming, there are three possible methods for identifying causes:

1. the random method
2. the systematic method
3. the process analysis method

The random method, during which team members randomly cite problems and probable causes, is a somewhat haphazard approach and may not identify all problem categories. However, it is useful as a general trouble-shooting technique and can help get the group in problem-solving mode.
The other two methods, systematic and process analysis, are more structured and rational in the identification of causes. These are used mostly by engineers and technicians.

The systematic method focuses analysis on one category at a time. Each category is examined in descending order of importance after the primary one is addressed.

The process analysis method looks at a production process identifying each sequential step, and the categories and causes for each step, one at a time.

When the cause-and-effect diagram has been constructed, the team or project manager can then suggest changes to the potential problem-causing areas. A series of experiments or additional statistical analysis may be necessary to determine the primary or root cause of a given problem.

The next step is to decide what corrective action is necessary. In the process of identifying the problem, the team suggests the desired outcome. By turning the diagram around, you can determine what impact the desired outcome will have on each of the listed categories and causes. In some cases you may find corrective action is required in one or all of the categories.

A machine in a process may require finer adjustment or even replacement if worn out. A newer machine may offer a leap in technology that may eliminate present quality control problems through greater automation or internal computer control processes.

The production or process method may require fine tuning, involving additional substeps before completion of a task. The layout of a process may also need reorganizing. Duties and responsibilities may need increased emphasis.

Stricter inspection and handling of raw materials may be necessary to ensure that they are of high standard. Improved selection of raw materials may also be required.

Changes to the measurement process may be necessary, such as more accurate measurements, increased frequency of inspection, and introduction of new statistical methods for analysis.

Perhaps current personnel are inadequately trained in both their job and in quality control. Upgrading job skills may be necessary. It is also possible that declining quality is due to poor work habits or boredom with the job.

Once the root cause of the problem has been identified and the effects of the desired outcome on other areas of the project have been studied, appropriate corrective action is taken. At this point, change requests are processed and safeguards set in place to prevent future recurrences.

Even when a problem has multiple sources, you will find cause-and-effect diagrams are invaluable in pinpointing them all. Flowcharting with cause-and-effect diagrams is an effective way to conceptualize causes to a problem in a project or process. Once flowcharted, the problem can be further analyzed using other analytical tools. Ultimately, corrective action and protective safeguards are applied to solve the problem and prevent future recurrences.

Flowcharting for Project Quality Assurance

It's usually beneficial to approach project problems in new ways. One effective technique you can use when addressing problems related to project quality assurance is flowcharting. You can use this method of problem solving to visually map the process or problem in question.

Flowcharts graphically represent processes and activities. They can help you identify the source of specific problems, which will enable you to find solutions. In addition, they can make communication about problems easier, help you discipline your thinking, and show how different elements fit together.

You can use two types of flowcharts for quality assurance purposes—the cause-and-effect diagram, and the process flowchart. Details about these two types of flowcharts are provided below.

1. Cause-and-effect diagrams
For every quality-related effect or problem in a project, a cause must be identified. Cause-and-effect diagrams can help you establish a cause, whether it is a problem or a desirable result an organization has found and wants to reproduce. These diagrams are also called fish-bone diagrams, because they resemble a fishbone with branches slanting off a main "spine."

When causes are established, they are categorized according to type. Cause types can include such things as materials, machines, people, and information. They are represented with a branch on the fishbone diagram. All subcauses connect to these branches.

Cause-and-effect diagrams are useful in brainstorming sessions because they act as visual displays for dividing large problems into manageable parts. Listed below are the four steps for constructing a cause-and-effect diagram.

• Identify the problem or effect. To identify the problem or effect, place a concise statement of the problem in a box at the end of a horizontal line.
• Identify the causes. Next, in a brainstorming session, identify any causes for the problem. Focus discussions on one cause at a time. Possible subcauses are identified at this time as well.
• Build the diagram. In the third step, build the diagram. To do this, organize the causes and subcauses into the diagram layout. Each branch should represent a cause-type, such as materials, machines, and information. Connect subcauses to these branches.
• Analyze the diagram. Finally, analyze the diagram. Identify the logical solutions by considering whether each solution is achievable.

2. Process flowcharts
Flowcharts also indicate what is done throughout a process, from one step to another. On these process flowcharts, information about a process is placed inside or beside an appropriate symbol.

With some training, anyone on a quality improvement team can draw a process flowchart. However, everyone should clearly understand the meaning of each symbol used on the flowchart, including the symbols for Operation (a rectangle), Movement/Transportation (an arrow), Decision Point (a diamond), Inspection (a large circle), Paper Documents and Delay (both specialized rectangular symbols), Boundary (an oval), and Connector (a small circle).

To create a process flowchart, you draw a picture of the process. With some training and practice, flowcharting can be a straightforward process. Follow the steps listed below to complete this task.

• Define the process steps. First, you should identify the steps in a process by holding a brainstorming session and letting everyone on the team provide input.
• Sort the steps in order. Next, identify what is done at each step and then sort the steps in order.
• Place the steps in the appropriate symbols. The third step involves placing each step in the appropriate symbol. Use standard symbols to sketch the flowchart.
• Evaluate the steps. Finally, reevaluate the steps. This will ensure that the process is complete, efficient, and free of problems. Be sure to review the actual process and then make any necessary revisions to the flowchart.

Flowcharts are effective tools for enhancing the quality assurance of a project, as they graphically represent processes and activities. They can help you identify the cause of a problem or effect, and identify problems in a process.