This lab will deal with hypothesis tests. In this lab, you will use software to calculate
summary statistics for data, and then use those summary statistics to conduct a
hypothesis test by hand.
Goals for this assignment:
• Use R to generate summary statistics
• Practice calculations for hypothesis tests by hand
• Interpret results of hypothesis tests
Grading: there are four possible points for each skill objective and analysis objective.
Activity 1
In previous labs, we looked at a research paper from 1983 by Chambers, Cleveland,
Kleiner, and Tukey examining the effectiveness of cloud seeding using silver nitrate.
Total rainfall (in acre-feet) was measured for 26 seeded clouds and 26 unseeded
clouds. We will again be examining this data set further.
We would like to use a hypothesis test to assess whether cloud seeing is effective. As
we have small sample sizes, we need to be able to assume our data is approximately
normally distributed. In a previous lab, you showed that the histograms for this data
are extremely skewed. However, many of you noted that using a log transformation
resulted in data that looked approximately normally distributed.
Skill Objective: Use R to take a log transformation of the rainfall data. Then,
use R to calculate the means and standard deviations for the log of rainfall for
seeded clouds, and for unseeded clouds.
Analysis Objective: Using these results, conduct a hypothesis test to determine
whether there is evidence that cloud seeding increases rainfall.
