Statistical Quality Control

As consumers, we take many things into consideration before purchasing a product or service.  For example, we often consider the price of the product or service to ensure we are getting good value for our money.  But another important factor we consider is quality.  The quality of a product or service, which is the degree to which a product or service meets its specifications, is a major issue for both the provider of the product or service and the customer.  Poor quality may result in the producer recalling the product, which may cost the producer a significant amount of money.  Similarly, poor quality may be expensive for the consumer or discourage potential customers from purchasing the product or service altogether.

Not surprisingly, quality is an important part of businesses that manufacture products, ensuring that the product meets the required specifications.  Manufacturing firms employ quality control tactics, such as inspections and measurements, to monitor the production process.  Among other things, these quality control processes ensure that the product is free of defects, that the product is delivered at the right time and to the right place, and that the product is sold at the right price.  When the quality standards are not met, preventive or corrective action is taken to move the production process back into compliance.

But quality is just as important to businesses that provide services, such as banking, healthcare, and education.  In the service sector, quality is applied to ensure that the service provided meets the needs and expectations of the customer.  In the service industry, quality control tactics, such as monitoring timelines for providing service or customer satisfaction surveys, focus on improving customer service and customer satisfaction.

Although there are other ways to measure quality, this chapter focuses on statistical process control.  The goal of statistical process control, which utilizes a graphical display called a control chart, is to monitor a process and then determine if the process can continue or if corrective action must be taken to meet the desired level of quality for the process.