Statistics 101 – Homework 2
Due Friday, September 9, 2005
Homework is due on the due date at the end of the lecture.
Reading:
August 29 – September 2
September 7 – September 14
Chapter 5
Chapter 6
Assignment:
1. On homework 1 the birth weights of 44 babies born at a Brisbane, Australia
hospital were summarized in a frequency table. Eighteen of those babies were
girls. Their birth weights, in grams, are given below.
3,837 3,334 2,208 2,576 3,208 3,746 3,523 3,430 3,480
3,116 3,428 2,184 2,383 3,500 3,866 3,542 3,278 1,745
a) Answer the questions, Who? What? When? Where? Why? How? for these
data.
b) Make a stem-and-leaf display of the baby girls’ birth weights.
c) Using the stem-and-leaf display, describe the distribution of birth weights for
baby girls. Make sure you mention the shape, center, spread and any outliers
or other interesting characteristics of the distribution.
d) Calculate the sample mean birth weight.
e) Calculate the sample median birth weight. Why is the sample median birth
weight greater than the sample mean birth weight?
f) Calculate the five number summary for these data.
g) Given the value
∑(y − y) =
2
6,781,240.5, calculate the sample standard
deviation for these data.
h) Which do you think provides a more informative summary of these data; a
five number summary or the sample mean and sample standard deviation?
Briefly explain your answer.
The remaining twenty-six babies were boys. On the next page is JMP output for the
distribution of baby boy birth weights.
i) Describe the distribution of birth weights for baby boys. Make sure you
mention the shape, center, spread and any outliers or other interesting
characteristics of the distribution.
j) Give the value of the sample mean birth weight for boys. Give the value of
the sample median birth weight for boys.
k) Give the value of the sample standard deviation for boys.
l) Construct side-by-side box plots (use a common scale) and use these to
compare the distribution of girls’ birth weights to boys’ birth weights.
1
Birth Weight
6
2
Count
10
Stem
4
4
3
3
3
3
3
2
2
2
2
2
Leaf
2
Count
1
889
66677
4444455
22333
0
89
6
3
5
7
5
1
2
1
1
1
15002000 2500 3000 3500 40004500
2|1 represents 2100
Quantiles
100.0%
75.0%
50.0%
25.0%
0.0%
Moments
maximum
quartile
median
quartile
minimum
4162.0
3645.0
3404.0
3162.0
2121.0
Mean
Std Dev
N
3375.3077
428.04605
26
2. (JMP assignment) Data are obtained on the time between nerve pulses along a
nerve fiber. The time is rounded to the nearest half and the units of measurement
are 1/50th of a second. For example, the value 30.5 represents 30.5/50 = 0.61
seconds. The data are available on the course web page both as a JMP (.JMP) file
and a straight text (.TXT) file. Follow the directions in the JMP Guide to
download the file and create output. Make sure to print the output and turn it in
with your assignment. Use the output in answering the following questions.
a) Describe the shape of the distribution of time between nerve pulses.
Based on this description would you expect the mean to be equal to, less
than, or greater than the median? Briefly explain your answer.
b) Looking at the histogram, are there any apparent outliers? If so, what are
their values?
c) Give the five number summary for the time between nerve pulses.
d) Looking at the box plot, are there any apparent outliers? If so, what are
their values?
e) Calculate the sample range and sample IQR for these data.
f) Give the sample mean and sample standard deviation for these data.
g) Did JMP split the stems in the stem-and-leaf plot?
h) Look at the raw data in the JMP data table and look carefully at the stemand-leaf plot. What did JMP do to the data before constructing the stemand-leaf plot?
2