Lesson 7

Discover

 

It is usually not possible to test every single product, survey every member of a population, or examine every single situation.

 

In previous lessons, you looked at how quality control departments use statistics to set standards based on collected data. This information helps ensure that products meet company standards and the standards set by regulatory agencies (e.g., government). But how much product has to be sampled to instill sufficient confidence in the statistical data and, ultimately, confidence in the safety of the product?

 

For example, does every bottle of orange juice leaving a plant need to be tested by a quality control department in order for the consumer to be confident that the product is safe? Does every jar of jam need to be checked to ensure that it has the correct amount of jam in it so the consumer feels he or she receives fair value? Does every millilitre of water leaving a wastewater treatment facility have to be tested to be confident that the water is safe for the environment?

 

Statisticians and quality control technicians have to determine how large of a sample they need to test so they can be sufficiently confident in the results. A pharmaceutical manufacturer, for example, needs to determine how many drug capsules should be tested to have an acceptable level of confidence that all of the capsules produced are safe and effective. There is a fine line between testing enough product to be confident that the drugs are safe and testing too much product because this can get expensive and waste product.

 

Try This 1

 

Use the Sample Size applet to investigate what sample sizes would be required for a given population, confidence intervals, and confidence levels.