Stat 301
Lab 2
Due September 15, 2014
Last week's lab looked at data on the heights of children ages 3 to 19. The data are
available on the course Web site:
http://www.public.iastate.edu/~wrstephe/stat301.html
In this week’s lab assignment we will look at whether gender of the child can explain
some of the variability in children’s heights. You should use JMP to perform an analysis
to compare the heights of Males to those of Females. It is not sufficient to simply hand
in JMP output. You must answer the questions completely. Turn in the JMP output
attached at the end of your written answers.
1. Two-sample problem.
a) Summarize the heights graphically and numerically for each gender. How do male
heights compare to female heights?
b) Are males significantly taller than females in terms of population mean heights?
Perform the appropriate test of hypothesis. Use α=0.05.
c) Report the value of a 98% confidence interval for the difference between the
population mean height for males and the population mean height of females.
Give an interpretation of this interval.
d) Is the confidence interval in c) consistent with your test of hypothesis in b)?
Explain briefly.
e) Use JMP to create the residuals for the two genders, male and female. Use
Analyze + Distribution to create JMP output that looks at the distribution
(histogram, box plot and Normal Quantile Plot) of the resulting 100 residuals.
f) Refer to the histogram of residuals and indicate what you see and what this tells
you about the condition that the random errors are normally distributed.
g) Refer to the box plot of residuals. Are there any possible outliers? If so, what are
the corresponding heights and genders? What does the box plot tell you about the
random errors being identically distributed?
h) Refer to the Normal Quantile Plot of residuals and indicate what you see and what
this tells you about the condition that the random errors are normally distributed?
i) Comment on whether or not the data are consistent with the condition that both
populations (male and female) have the same standard deviation. This will
require further analysis with JMP.
j) Summarize what you have learned about the conditions necessary for statistical
analysis of the data on heights from your analysis of residuals.
2. On a separate piece of paper (this sheet will be graded separately from your answers
to part 1) write a brief summary of what you have learned about heights of male and
female children between the ages of 3 and 19.