Learn by Doing – Proportions (Step 3) Understanding P-values

Published: October 22nd, 2013

Category: Activity 1: Learn By Doing

Complete the following activities to test your understanding of p-values.

In 2007, a Gallup poll estimated that 45% of U.S. adults rated their financial situation as “good.” We want to know if the proportion is smaller this year. We gather a random sample of 100 U.S. adults this year and find that 39 rate their financial situation as “good.” Use the output from Minitab to complete the following statements about the p-value. Use numbers from the output to fill in the blanks.

Test and CI for One Proportion. Test of p = 0.45 vs p < 0.45 Sample: 1: X = 39 N = 100 Sample p = 0.390000 95% Upper Bound = 0.485600 Z-Value = -1.21 P-Value = 0.114

The trustees of a local school district commission a survey to determine voter opinions about a possible bond measure to fund school upgrades. In a poll of 293 of the district’s 5,019 registered voters, 178 would support the bond measure. A hypothesis test was conducted using Minitab to determine if such a bond would pass with the required 55% of the vote.

Minitab output: Test and CI for One Proportion Test of p=0.55 vs p > 0.55 Sample: 1 X: 178 N: 293 Sample p: 0.607509 95% Upper Bound: 0.66342 Z-Value: 1.98 P-Value: 0.024

Do zinc supplements reduce a child’s risk of catching a cold? A medical study reports a p-value of 0.03. Are the following interpretations of the p-value valid or invalid?

This document is linked from Proportions (Step 3).