Lesson 5

Lesson 5 Summary

Quality control departments are the gate keepers of the manufacturing process. They make sure that the product leaving a facility is safe and that it meets the company’s standards and the customer’s expectations.

Quality control technicians need to make well-informed decisions. For data that is normally distributed, quality control technicians can use normal curves and z-scores to help them make decisions. For instance, technicians can help companies to determine how much of the product is meeting specifications or standards. This information is also useful for companies trying to set standards or determine warranty periods. If the standards are too narrow or the warranties too long, the company has to discard a lot of product and loses money. If the standards are too wide or warranties are too short, the company may have a lot of customer complaints.

The normal distribution can provide companies with valuable information that can be used to improve processes. For example, you discovered that if the OJ Juice Company decreased the standard deviation for the volume of juice in its 500-mL bottles, a larger percentage of the product coming off the production line would meet the new quality standard of between 499.0 mL and 500.5 mL.

Z-scores and the normal distribution can also help companies to determine what length of warranty to offer on a product.

In the next lesson you will look at the importance of confidence in the interpretation of statistical data.