CSI Informed Decision Project
Modesto Junior College
(Chanel Dragnet) Bum-de-bum, bum..........Ladies and gentlemen: the story you are about to hear is true. Only the facts
have been changed to protect the innocent.
Last semester someone broke into the Science and Math Division Dean’s office and made changes to the upcoming work
assignments. They hoped the secretary would input the changes into the computer believing they were updates by the
dean. Why would someone do this you ask? The dean has implemented a new block schedule for math and science so
our science majors can easily enroll in all the required classes they need. This plan requires some faculty and staff to
work on FRIDAYS! (gasp... horrors of horrors!!) Someone went in and changed the assignments so a different group of
faculty and staff than the dean originally assigned had the FRIDAY classes!
Once the secretary noticed the unauthorized changes, she realized the muddy trail of foot prints into the dean’s office
MUST have been made by the rascally rat who made the changes. She carefully recalled WHO had access to the dean’s
office and had the dean call them all in for a line up. (see the poster and SHOE PRINT outside my office)
Our dean has asked the statistic classes to use our powerful methods of data analysis to tell him WHO the culprit is!
To this end, you will use the CSI project data set in our class group in StatCrunch.
One more note. The faculty union representative got wind of this and has FORBIDDEN any measurements taken from
ANY faculty, staff or the suspects themselves. The suspects have been instructed if they see someone approaching them
with a tape measure to RUNNNNNN!
The CSI project data set has these variables: Height measured to nearest quarter inch, shoe length measured to the
nearest tenth of a centimeter, sex and age.
Copy and paste the rest of this document into a word document and type in your answers leaving a blank space
between the prompt and your response. You will copy and paste the computer output when asked as well. Turn this
in with your name, my name and the title of the project at the top of the page. NONE of this assignment is put into a
StatCrunch Report. None of this assignment is shared with the class group on StatCrunch.
Here are the things you should do to build your data driven argument. You will need to refer to your Lab 4 directions on
how to make a good histogram and get summary stats:
1. Your CLUE will be to determine if the culprit’s shoeprint is more likely to be a man’s or a woman’s:
A. Get the summary stats and make well-made relative frequency histograms for the shoe length that has the
mean as its center and bars equal to one standard deviation wide. (see lab 4 directions for the details-we
will also show how to do this in our 135 section). Since sex is a major lurking variable you should analyze
the men separate from the women by selecting “Sex” in the Group By prompt. Once you have the graphs
made-be sure to carefully follow lab 4- (and summary stats) select OPTION/Copy. Follow the directions in
the pop up window that appears to copy and paste the summary stats into the document here. Print the
two histograms on separate pages.
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B. The histograms (if made correctly) will show the percentage of data within 1, 2 and 3….standard deviations
of the mean as each bar is one standard deviation wide. Use this information and the Empirical Rule to
explain why both the men and women’s shoe lengths are approximately Normally Distributed.
C. Use the conclusion that the men’s distribution is approximately Normal to find how many standard
deviations above or below the mean the observed culprit’s shoe print is IF it is a man’s.
D. Use the conclusion that the women’s distribution is approximately Normal to find how many standard
deviations above or below the mean the observed culprit’s shoe print is IF it is a woman’s.
E. EXTRA CREDIT- What’s the probability a randomly selected print this size is from a male? What’s the
probability a randomly selected print this size is from a female? (HINT: you will have to consider a tail area
as there is no area under one number in continuous probability distributions). Interpret each of these
probabilities in a sentence.
F.
Is the shoeprint more likely a man’s or a woman’s? Give a data driven argument. This is your first clue to
which of the suspects is the true culprit!
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