Answer to Question #2999 in Statistics and Probability for sushma bhargav
b) What are the limitations of a quality control charts?
Quality is a much more complicated term than it appears. Dictionary definitions are usually inadequate in helping a quality professional understand the concept. It seems that every quality expert defines quality is a somewhat different way. There are a variety of perspectives that can be taken in defining quality (e.g.customer's perspective, specification-based
Are there commonalities among these definitions?
Is any one definition "more correct" than the others?
Is one quality expert "right" and the others "wrong"?
Quality professionals constantly debate this question.
The editors of Quality Digest say that defining the word "quality" is "no simple endeavor." They asked, in their December 1999 issue, for readers to send them their definitions of quality to be gathered and posted on Quality Digest Online.
A modern definition of quality derives from Juran's "fitness for intended use."This definition basically says that quality is "meeting or exceeding customerexpectations." Deming states that the customer's definition of quality is the onlyone that matters.
Quality assurance (QA) is a broad concept that focuses on the entire qualitysystem including suppliers and ultimate consumers of the product or service. It includes all activities designed to produce products and services of appropriatequality.
According to ASQ, QA includes all those planned or systematic actions necessaryto provide adequate confidence that a product or
service will satisfy given needs.
Quality control (QC) has a narrower focus than quality assurance. Quality control focuses on the process of producing the product or service with the intent of eliminating problems that might result in defects.According to ASQ, QC includes the operational techniques and the activitieswhich sustain a quality of product or service that will satisfy given needs; also the use of such techniques and activities.
Quality management is the totality of functions involved in the& determination and achievement of quality (includes quality assurance and quality control).
A number of scholars in the quality field have developed lists of dimensions that define quality for a product and/or a service. David Garvin developed a list of 8dimensions of product quality. Evans and Lindsay provide a list of 8 dimensions of service quality. These are general lists and serve as good starting points. But,current research indicates that in terms of service quality, the dimensions are different for different industries. So Evans and Lindsay's list may not apply equally well to, for example, health care services and food services. Parasuraman,et. al. developed a general list of 5 service dimensions that they tested in 4 types of service industry, but
the applicability of these dimensions in other industries is unknown.
b) What are the limitations of a quality control charts?*
The limitations of a quality control charts:
The quality control chart is based on the research of Villefredo Pareto. He found that approximately 80 percent of all wealth of Italian cities he researched was held by only 20 percent of the families. The Pareto principle has been found to apply in other areas, from economics to quality control.
Pareto charts have several disadvantages, however. Based on the Pareto principple, any process improvement should focus on 20 percent of issues that cause the majority of problems in order to have the greatest impact. However, one of the disadvantages of Pareto charts is that they provide no insight on the root causes. For example, a Pareto chart will demonstrate that half of all problems occur in shipping and receiving.
Failure Modes Effect Analysis, Statistical Process Control charts, run charts and cause-and-effect charts are needed to determine the most basic reasons that the major issues identified by the Pareto chart are occurring.
Multiple Pareto Charts May Be Needed
Pareto charts can show where the major problems are occurring.
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