Dr. Brenda Masters

Lesson 14 covers Inferences on the Population Mean when the Population Standard Deviation is known.  The resulting hypothesis test and confidence interval are based on the Z-distribution, also called the Standard Normal Distribution. Lesson 15 covers Inference on the Population Mean when the Population Standard Deviation is unknown.   The sample standard deviation, S, will be used as an estimator for sigma, the population standard deviation, but when that occurs the test statistic is not Z, but t and the confidence interval form is also based on t, not Z.   Here are some details, Class Notes Z test and t test, with CI equations .