Statistics 101: Section L - Laboratory 2
In today’s lab we will collect more data, this time on two variables that may be related. We
will also look more closely at the distribution of data using the statistical package JMP.
Activity 1: The idea of variation is fundamental to the understanding of statistics. Your
group will be doing basic research in morphology, the study of form and structure in plants
and animals. You are going to measure the length of both your left forearm and your left
foot. Humans have two bones in the forearm, the ulna and the radius. To make sure everyone
is measuring the same bone, we will all measure the length of the left ulna. To do this, place
your left forearm palm down on the table in front of you. The ulna is the bone on the outside
of your forearm. One end of the ulna is the larger portion of the elbow; the bone closest to
the table. The other end of the ulna is the small bone on the outside of the left wrist. This
bone sticks out a little bit for most people.
Take a tape measure and measure the distance (in cm) between these two points. Record
the name, sex, and left forearm (ulna) measurement on your group answer sheet.
Once you have measured everyone’s forearm, you will also need to measure the foot length of
each group member. To make these measurements uniform throughout the groups, measure
the length of your left foot with your shoe off. Record these measurements on the group
answer sheet. Be sure that your foot measurement is paired with your forearm measurement.
Activity 2: In this activity, we will look more closely at the distribution of the M&M data
we collected in Lab 1. This will be done in the computer lab in Snedecor 321. On the
desktop, double-click on the JMP icon. Once the JMP program has started, follow along as
we go through the directions below.
1. From the JMP Starter window, choose the File tab and click on Open Data Table.
Go to C: → statLabsLocal → Stat101L and click on Lab1S04.JMP. This should open
a spread sheet with data collected last week in Lab 1.
2. Note that some of the columns have entrees that are left justified (close to the left edge
of the column) and some are right justified (close to the right edge of the column).
Double click on the Group column. Note the Data Type and Modeling Type. Double
click on the Number column. Note the Data Type and Modeling Type. Data Type
and Modeling Type are very important and control the types of analyses JMP will do
automatically. Be sure to use Data Type: Character and Modeling Type: Nominal for
variables that indicate categories or groups. Be sure to use Data Type; Numeric and
Modeling Type: Continuous for variables that indicate count or measurement values.
Close the windows for Group and Number by clicking on OK.
3. Go back to the JMP Starter and click on the tab Basic Stats. The first option is
Distribution. You can get to Distribution from the Analysis pull down menu or
by clicking on the icon that looks like a sideways green shaded bar chart. Click on
Distribution, Highlight NetWgt by clicking on it under Select Columns and then
click on Y, Columns. This will cast the NetWgt into the role of a response variable
(a Y, Column). You can also do this by double clicking on NetWgt under Select
Columns. Click on OK. A window should pop up with the distribution of NetWgt.
4. Click on the red triangle pulldown next to NetWgt. Choose Display Options →
Horizontal Layout. Click on the red triangle pulldown next to NetWgt again. This
time choose Histogram Options → Count Axis. Click on the red triangle pulldown
next to NetWgt again and choose Stem and Leaf.
5. Go to the icon tool bar at the top of the main window and click on the hand (grabber)
tool. Go to the histogram, click on the tallest bar and drag towards the horizontal
axis. Stop when you have bars that fill up the unit intervals.
6. From the JMP menu, select File → Print.
Activity 3: You will be given the data collected on the forearm and foot measurements.
Enter the data into a New Data Table in JMP. Note that a new data table starts out
with only one column. You can add additional columns by going to the red triangle pull
down next to Columns. You can add one column at a time using New Column or several
columns using Add Multiple Columns. Be sure you have the correct Data Type and
Modeling Type for the three variables; Gender, Forearm and Foot. Once you have entered
the data, use Distribution to analyze the data on Forearm length and Foot Length. Print
off a copy of the output. You will need this to answer the questions for the lab.
Questions for Activity 2: Turn in the JMP output with your answers.
1. Describe the distribution of the net weight of the M&M bags.
2. Give the mean and median of the net weight of the M&M bags.
3. Based on the analysis of the 110 net weights, how would you label a similar bag of
M&Ms? Explain briefly your reasoning.
Questions for Activity 3: Turn in the JMP output with your answers.
1. Referring to the stem and leaf plot, describe the distribution of the forearm measurement.
2. On the stem plot denote the mean forearm measurement and the median forearm
measurement.
3. Referring to the histogram, describe the distribution of the forearm measurement.
4. On the histogram denote the mean forearm measurement and the median forearm
measurement.
5. Which graphical representation of the data do you prefer, the stem and leaf plot or the
histogram? Explain briefly your choice.