Graveyard Activity Wrap-up
July 1, 2008
1. Hypothesis: Write down the hypothesis your group decided on earlier.
If your hypothesis is correct, then if we look at tombstones with the same amount of
weathering:
The igneous stones will be _________ older/younger than the metamorphic stones and
_________ older/younger than the sedimentary stones; and the metamorphic stones will
be _________ older/younger than the sedimentary stones.
2. Each group has analyzed their own small data set. What did you conclude based on
that analysis?
3. We will analyze the graveyard data from all the groups. We will use the
statistical software Minitab to analyze the data. Open the Minitab software by
double-clicking on the icon.
Open a web browser and go to http://www.mtsu.edu/~lbgreen/Activities/MSP.html. Near
the bottom of the page, you will see two Excel files. One has the graveyard data for each
group, the other has the same data, with duplicate entries removed. Open that file, named
GraveyardClean.xls. Copy the data into the Minitab worksheet. (NOTE: If all of the
column headings change name to C1-T, C2-T, etc, that means that you copied the column
name into a data cell. Make sure that you put the name into the blank cell at the top of
the column. The only columns that should have “-T” are the text columns: ROCK and
NAME OF DECEASED.)
4. Age: Go the Graph menu and select Histogram. A window will open. Select Simple,
then click OK. Another window will open. Under “Graph Variables”, click in the empty
box, then double-click AGE in the box on the left to select it. Then click OK. This
histogram shows the distribution of the ages of the gravestones in our data set. Describe
it. What range of ages do we have in our data set? Which ages are most typical?
5. Age and Weathering: Go to the Graph menu and select Scatterplot, then Simple.
Under the “Y” variable, select AGE; for the “X” variable, select WEATHERING. Then
click OK. Describe the graph you obtained. What does this graph tell us about the
relationship between age and weathering?
Go to the Graph menu and select Dotplot, then With Groups. Under “Graph Variables,”
select AGE; under “Categorical Variables for Grouping,” select WEATHERING. Then
click OK. Compare the result to the graph that you just obtained above.
6. Age and Weathering by Rock Type: We’d like to look at graphs of ages and
weathering amounts for each rock type separately. To do this, we will create new
columns of data. Go to Data, then Unstack Columns. In the “Unstack the data in” box,
select all of the columns. In the “Using data in:” column, put the ROCK variable. Under
“Store unstacked data:,” select the option for a new worksheet. Then click OK.
You will now have a second worksheet. The column names for this worksheet will be
the same as the original column names, with the addition of rock type. Notice that there
are three sets of new columns, one for each rock type.
Repeat the steps in number 5 to make graphs (either scatterplots or dotplots, you decide)
of AGE and WEATHERING, one for each individual rock type. Compare these graphs.
Describe them. What can you conclude from these graphs? Does the data support your
hypothesis?
7. Age by Rock Type: Repeat the steps you followed in number 3 to obtain histograms
of the ages of the gravestones for each individual rock types. Compare these graphs to
each other and to the histogram that you got in 3. What do you observe?
The original hypothesis concerned weathering rates and rock types, so why are we having
you check age by rock type, with no weathering numbers? How does this advance our
understanding of the data set?
8. Describing the set with numbers. Go to the Stat menu and select Basic Statistics,
then Display Descriptive Statistics. Under “Variables,” select the three AGE columns
and click OK. Use the output to fill in the following table:
Number
Mean Age
Standard
Deviation of
Age
Igneous
Metamorphic
Sedimentary
Recall that most of the data lie within two standard deviations of the mean. Calculate the
numbers that are two standard deviations away from the mean for the following values:
AGE
Lower
Igneous
Metamorphic
Sedimentary
Upper
Compare what these values imply to the histograms that you made in number 7.
9. Descriptive Statistics by Rock Type: Go to the Stat menu again and select Basic
Statistics, then Display Descriptive Statistics. This time, under “Variables,” select
AGE_I (or whatever the age column for igneous rock type is called). Under “By
Variables:,” select WEATHERING_I. You will get the statistics divided into categories.
Repeat this for the other rock types, and complete the following table:
Igneous
Mean Age
St. Dev. Age
Metamorphic
Mean Age
St. Dev. Age
Sedimentary
Mean Age
St. Dev. Age
Weathering = 1
Weathering = 2
Weathering = 3
Weathering = 4
Weathering = 1
Weathering = 2
Weathering = 3
Weathering = 4
Weathering = 1
Weathering = 2
Weathering = 3
Weathering = 4
Recall what you wrote in number 1. Is your hypothesis supported?
10. Further Research: What issues did we discover about our data set? What issues
would a skeptical colleague have with your data gathering method? If your hypothesis
was supported, was the support strong enough to convince a skeptic? If your hypothesis
was not supported, was the contradiction strong enough to make you change your
hypothesis, or do you think that you could support this hypothesis with data gathered in a
different way?