Oak Trees

Math/BA 256,

Part A. Construct a histogram of acorn size of oak trees in the Atlantic Region, using your calculator.

1. Describe the shape of the distribution.

2. Which method of describing the center and spread of this distribution is better? (mean & standard deviation or 5 number summary) WHY?

3. Find either the 5 number summary or the mean and standard deviation. Whichever you thought was the better choice.

Part B. We theorize that oak trees with large acorns will have larger ranges because the acorns are more likely to be picked up and moved by larger animals that have larger ranges.

1. What is the explanatory variable? What is the response variable?

2. Make a scatter plot for oak trees in California, using your calculator. What do you see? Does there seem to be a clear pattern?

3. Does it look like a positive or negative association?

4. To measure the strength of this association, calculate the r-value for this data.

5. The last species in the list is an outlier. Quercus tomentella Engelm has a range limited to the Channel Islands off the California coast. Which other species in the list might also be an outlier?

6. Remove the data points for the two outliers from our data and recalculate your r-value.

7. Is the correlation coefficient a resistant measure? What parts of the formula we use to calculate r might suggest this?