1. The data set video.xls contains responses for the following survey from the class:
a. Approximately, how many
movies do you typically rent (or share the rent for) per week
during the school year?................................................................................
b. Approximately how many
of these (see Part a) do you typically view to the end after
renting them?.....................................................................................
2. Use your calculator and Excel to compute the standard
deviation of the sample of rental
values and the sample
of view values.......
Rental Values __________
View Values ___________
3. Are the relative magnitudes of the mean rental
value and mean view value
reasonable? Explain.
4. Describe behavior that would cause the standard
deviation of view values to
exceed the standard deviation
of rental values.
5. Use the random number table to select a random
sample of 4 rental values, then
compute the standard deviation
of this sample by hand..__________________
In Excel click TOOLS, then DATA ANALYSIS,
then SAMPLING. In the window that
appears, indicate the range of the population
of rental values (if you used a cell for a variable
name for the rental rates and you include it
in your range for the population, be sure to check
the Labels box.) The sampling method we will
use is Random (which is checked already as
the default). Please note that Excel asks for
the number of samples but really wants to know
the number of observations to put in your sample.
To avoid confusion, we will not
use the term "sample" interchangeably with
"observation" in class. For us, a sample
is a set of observations that is a subset
of a population. In this case we want four
observations. You have three options for the
destination of your random sample.
The default of a new worksheet often proves to
be convenient.
6. Interpret the value you computed in Question 5.
7. Suppose the class is a representative sample of
WCU students and that the
students rented these movies
in Sylva or Cullowhee. Estimate the total number of
rentals by 7000 WCU students
for a local video store owner.
8. We could estimate the standard deviation for all
7000 students as 7000 times
the individual standard deviation.
If the weekly renting values are bell-shaped, use
the Empirical Rule to inform
the video store owner about the number of WCU
student rentals that are likely
to occur during a randomly selected week.
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