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Margin of Error in Regression. In Exercises14.109and14.110, you will examine the magnitude of the margin of error of confidence intervals and prediction intervals in regression as a function of how far the specified value of the predictor variable is from the mean of the observed values of the predictor variable.
14.109 Age and Price of Orions. Refer to the data on age and price of a sample of 11 Orions given in Table 14.4 on page 572
a. For each age between 2 and 7 years, obtain a95%confidence interval for the mean price of all Orions of that age. Plot the confidence intervals against age and discuss your results.
b. Determine the margin of error for each confidence interval that you obtained in part (a). Plot the margins of error against age and discuss your results.
c. Repeat parts (a) and (b) for prediction intervals.

Short Answer

Expert verified

Part a)

Look at the figure confidence intervals are shaded by yellow color

The regression equation is not fitted well, because only one point is not within the bands of the confidence interval.

Part b)

There is a non-linear relationship found between the margin of error and age

Part c)

Repeat part (a)

Look at the figure, the regression equation is fitted well because all ages are within the bands of the prediction interval.

Repeat part b)

There is a nonlinear relationship found between margin of error and age.

Step by step solution

01

Part a) Step 1: Explanation

Let xis the age in years.

Let yis the price in$100

Obtain a 95\% confidence interval for the mean price of all Orions of that age.

Using Minitab follow the steps for finding the 95%confidence intervals.

1. Enter data into Minitab Worksheet.

2. Click Minitab Enable commands for getting commands used in finding confidence intervals through regression.

3. The obtained Minitab partial output for the 95%confidence intervals is,

Figure 1

Look at the figure 95%confidence intervals are shaded by yellow color.

02

Part a) Step 2: Explanation

Plot the confidence intervals against age.

Minitab commands:

The obtained output for the confidence intervals plot is,

Figure (2)

Look at the figure, the regression equation is not fitted well, because only one point is not within the bands of the confidence interval.

03

Part b) Step 1: Explanation

Find the margin of error for each 95%confidence interval obtained in part (a).

The formula for the margin of errorEis,

E=upperlimit-lowerlimit2

Using this formula in Minitab, the output for the margin of errors is;

Using the formula of Minitab the output of the margin error is

The scatterplot for the margin of error against age is

There is a non-linear relationship found between the margin of error and age

04

Part c) Step 1: Explanation

Obtain a 95%prediction interval for the mean price of all Orions of that age.

Using Minitab follow the steps for finding the 95%confidence intervals.

1. Enter data into Minitab Worksheet.

2. Click Minitab Enable commands for getting commands used in finding confidence intervals through regression.

3. The obtained Minitab partial output for the 95%confidence intervals is,

Look at the figure, 95%prediction intervals are shaded by yellow color.

Plot the prediction intervals against age.

The obtained output for the prediction intervals plot is,

Figure (2)

Look at the figure, the regression equation is fitted well because all ages are within the bands of the prediction interval.

05

Part c) Step 2: Explanation

Repeat part (b)

Find the margin of error for each 95%confidence interval obtained in part (a).

The formula for the margin of errorEis,

E=upperlimit-lowerlimit2

Minitab Command:

Using this formula in Minitab, the output for the margin of errors is,

The scatterplot for the margin of errors against age is,

Figure (4)

There is a nonlinear relationship found between the margin of error and age.

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Most popular questions from this chapter

In Exercises 14.48-14.57, we repeat the information from Exercises 14.12-14.21.

a. Decide, at the 10%significance level, whether the data provide sufficient evidence lo conclude that a is useful for predicting y:

b. Find a 90%confidences interval for the slope of the population regression line.

y=1.75+0.25x

In Exercises 14.70-14.80, use the technology of your choice to do the following tasks.

a. Decide whether you can reasonably apply the regression t-test. If so, then also do part (b).

b. Decide, at the 5%significance level, whether the data provide sufficient evidence to conclude that the predictor variable is useful for predicting the response variable.

14.70 Birdies and Score. The data from Exercise 14.34 for number of birdies during a tournament and final score for 63 women golfer are on the WeissStats site.

To find and interpret a confidence interval, at the specified confidence level 99%for the slope of the population regression line that relates the response variables to the predictor variable.

14.93 Corvette Prices. Following are the age and price data for Corvettes from Exercise 14.23.

x
6
6
6
2
2
5
4
5
1
4
y
290
280
295
425
384
315
355
328
425
325

a. Obtain a point estimate for the mean price of all 4-year-old Corvettes.

b. Determine a 90% confidence interval for the mean price of all 4-year-old Corvettes.

c. Find the predicted price of a 4-year-old Corvette.
d. Determine a 90% prediction interval for the price of a 4 -year-old Corvette.
e. Draw graphs similar to those in Fig. 14.11 on page 576 , showing
f. Why is the prediction interval wider than the confidence interval?

Corvette Prices. The Kelley Blue Book provides information on wholesale and retail prices of cars. Following are age and price data for 10randomly selected Corvettes between 1and 6years old.

Here, xdenotes age, in years, and ydenotes price, in hundreds of dollars.

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