Statistics 401
Lab 4 - Group Activity on Regression
Fall 2005
Group Answer Sheet
Names of Group Members
How long does a bar of soap last? Use JMP to analyze the data given to you on the weight
of a bar of soap on various days. Use the JMP output and your knowledge of regression
analysis to answer the following questions. Group members should discuss the questions
and come up with answers that are agreed on by all the group members. Turn in the group
answer sheet and one copy of the JMP output at the end of lab today.
1. Give the value and an interpretation within the context of the problem of:
(a) the estimated slope, β̂1 .
(b) the estimated Y-intercept, β̂o
2. Give the equation of the line relating day in use to weight.
3. Is there a significant linear relationship? Support your answer with either a test of
hypothesis or a confidence interval.
4. What is the predicted value and residual for a bar of soap used 7 days?
5. What is the estimated mean weight for bars of soap used 14 days? Also give a 95%
confidence interval for this mean weight.
6. How does the 95% prediction interval for a bar of soap used 14 days differ from the
confidence interval in 5? Be sure to indicate differences in interpretation as well as
value.
7. Comment on the plot of residuals versus day in use.
8. Comment on the analysis of residuals.