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The following table gives data on the mean number of seeds produced in a year by several common tree species and the mean weight (in milligrams) of the seeds produced. (Some species appear twice because their seeds were counted in two locations.) We might expect that trees with heavy seeds produce fewer of them, but what mathematical model best describes the relationship?

(a) Based on the scatterplot below, is a linear model appropriate to describe the relationship between seed count and seed weight? Explain

(b) Two alternative models based on transforming the original data are proposed to predict the seed weight from the seed count. Graphs and computer output from a least-squares regression analysis on the transformed data are shown below.

Model A:

Model B:

Which model, A or B, is more appropriate for predicting seed weight from seed count? Justify your answer.

(c) Using the model you chose in part (b), predict the seed weight if the seed count is 3700.

(d) Interpret the value ofr2 for your model.

Short Answer

Expert verified

(a) No, the linear model is appropriate to describe the relationship between seed count and seed weight .

(b) The answer to this part is given below.

(c) The seed weight if the seed count is 3700is 19.7760mg

(d) The value of r2for model is86.3%.

Step by step solution

01

Part (a) step 1: Given Information

We need to find the linear model appropriate to describe the relationship between seed count and seed weight or not.

02

Part (a) step 2: Explanation

No, The scatterplot shows a strong curved pattern.

03

Part (b) step 1: Given Information

We need to graphs and computer output from a least-squares regression analysis on the transformed data are shown.

04

Part (b) step 2:Explanation

Its scatterplot shows a more linear pattern and its residual plot shows no visible pattern.

05

Part (c) step 1: Given Information

We need to find the seed weight if the seed count is3700.

06

Part (c) step 2: Explanation

On the scatterplot, we that the variable on the horizontal axis is "ln(count)" and the variable on the vertical axis is "ln(weight)", so the variable is " while the -variable is " . The general regression equation is then:

lnweight=a+blncount

The constant is given in the row "Constant" and in the column "Coef" of the computer output of model B:

a=15.491

The slope is given in the row "ln(count)" and in the column "Coef" of the computer output of model B:

b=1.5222

Replacing with 15.491and with 1.5222in the general regression equation, we have:

lnweight=15.4911.5222lncount

Replace "count" by 3700and evaluate:

lnweight=15.4911.5222ln37002.9845

Take the exponential of each side:

weight=elnweight=e2.984519.7760

Thus the predicted weight is19.7760mg.

07

Part (d) step 1: Given Information

We need to find the value ofr2for in model.

08

Part (d) step 2: Explanation

About 86.3%of the variation in In(seed weight) is accounted for by the linear modal relating In(seed weight ) toIn(seed count.)

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