Learn by Doing – Z-Test for a Proportion

Published: October 22nd, 2013

Category: Activity 1: Learn By Doing

The objective of this activity is to give you guided practice in carrying out the z-test for the population proportion (p).

Background: This activity is based on the results of a recent study on the safety of airplane drinking water that was conducted by the U.S. Environmental Protection Agency (EPA). A study found that out of a random sample of 316 airplanes tested, 40 had coliform bacteria in the drinking water drawn from restrooms and kitchens. As a benchmark comparison, in 2003 the EPA found that about 3.5% of the U.S. population have coliform bacteria-infected drinking water. The question of interest is whether, based on the results of this study, we can conclude that drinking water on airplanes is more contaminated than drinking water in general.

Here is an example of possible output from software for this problem. We will verify the results ourselves.


This document is linked from Proportions (Step 4 & Summary).