- Slides: 9
Ishikawa diagram • Ishikawa diagrams are causal diagrams that show the causes of a specific event -- created by Kaoru Ishikawa (1990). • Common uses of the Ishikawa diagram are product design and quality defect prevention, to identify potential factors causing an overall effect.
• Causes are usually grouped into major categories to identify these sources of variation. The categories typically include: – People: Anyone involved with the process. – Methods: How the process is performed and the specific requirements for doing it, such as policies, procedures, rules, regulations and laws. – Machines: Any equipment, computers, tools etc. required to accomplish the job – Materials: Raw materials, parts, pens, paper, etc. used to produce the final product – Measurements: Data generated from the process that are used to evaluate its quality – Environment: The conditions, such as location, time, temperature, and culture in which the process operates
• Causes in a typical diagram are normally grouped into categories, the main ones of which are: 6 Ms: Men/people, machines, methods, materials, measures, mother nature. 4 Ps – Places, Procedures, People, Politics. 4 Ss – Surroundings, Suppliers, Systems, Skills.
Pareto Analysis • Pareto analysis is a statistical technique in decision making that is used for selection of a limited number of tasks that produce significant overall effect. • It uses the Pareto principle – the idea that by doing 20% of work, 80% of the advantage of doing the entire job can be generated. • Or in terms of quality improvement, a large majority of problems (80%) are produced by a few key causes (20%).
• This technique helps to identify the top 20% of causes that need to be addressed to resolve the 80% of the problems. • Once the top 20% of the causes are identified, then tools like the Ishikawa diagram can be used to identify the root causes of the problems.
Steps to identify the important causes using Pareto analysis • Step 1: Form an explicit table listing the causes and their frequency as a percentage. • Step 2: Arrange the rows in the decreasing order of importance of the causes (i. e. , the most important cause first) • Step 3: Add a cumulative percentage column to the table • Step 4: Plot with causes on x- and cumulative percentage on y-axis • Step 5: Join the above points to form a curve • Step 6: Plot (on the same graph) a bar graph with causes on x- and percent frequency on y-axis • Step 7: Draw line at 80% on y-axis parallel to x-axis. Then drop the line at the point of intersection with the curve on x-axis. This point on the x-axis separates the important causes (on the left) and trivial causes (on the right) • Step 8: Explicitly review the chart to ensure that at least 80% of the causes are captured
Some problems • Difficulties associated with Pareto Analysis: – Misrepresentation of the data. – Inappropriate measurements depicted. – Lack of understanding of how it should be applied to particular problems. – Knowing when and how to use Pareto Analysis. – Inaccurate plotting of cumulative percent data.