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Consider the model:

E(y)=β0+β1x1+β2x2+β3x22+β4x3+β5x1x22

where x2 is a quantitative model and

x1=(1receivedtreatment0didnotreceivetreatment)

The resulting least squares prediction equation is

localid="1649802968695" yÁåœ=2+x1-5x2+3x22-4x3+x1x22

a. Substitute the values for the dummy variables to determine the curves relating to the mean value E(y) in general form.

b. On the same graph, plot the curves obtained in part a for the independent variable between 0 and 3. Use the least squares prediction equation.

Short Answer

Expert verified

The mean value of E(y)for x1 = 0 isEy=β0+β2x2+β3x22+β4x3 andthe mean value of E(y)for x1= 1 is .Ey=β0+β1+β2x2+β3x22+β4x3+β5x22

Step by step solution

01

Dummy variable equation in general form

The mean value of E(y) in general form can be written for the value of x1 = 1 and x1= 0

For x1 = 0,Ey=β0+β1x1+β2x2+β3x22+β4x3+β5x1x22Ey=β0+β1×0+β2x2+β3x22+β4x3+β5×0×x22Ey=β0+β2x2+β3x22+β4x3

For x1= 1, Ey=β0+β1x1+β2x2+β3x22+β4x3+β5x1x22Ey=β0+β1×1+β2x2+β3x22+β4x3+β5×1×x22Ey=β0+β1+β2x2+β3x22+β4x3+β5x22

02

Graph

For the value of x2 = 0, the mean value E(y) least squares prediction equation will look like

E(y)=2+x1-5x2+3x22-4x3+x1x22E(y)=2+0-5×0+3×02-4x3+0×02forx1=0andx2=0E(y)=2-4x3

For the value of x2 = 0, the mean value E(y) least squares prediction equation will look like

E(y)=2+x1-5x2+3x22-4x3+x1x22E(y)=2+1-5×0+3×02-4x3+1×02forx1=1andx2=0E(y)=3-4x3

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Most popular questions from this chapter

Consider fitting the multiple regression model

E(y)= β0+β1x1+ β2x2+β3x3+ β4x4 +β5x5

A matrix of correlations for all pairs of independent variables is given below. Do you detect a multicollinearity problem? Explain


Suppose you fit the model y =β0+β1x1+β1x22+β3x2+β4x1x2+εto n = 25 data points with the following results:

β^0=1.26,β^1= -2.43,β^2=0.05,β^3=0.62,β^4=1.81sβ^1=1.21,sβ^2=0.16,sβ^3=0.26, sβ^4=1.49SSE=0.41 and R2=0.83

  1. Is there sufficient evidence to conclude that at least one of the parameters b1, b2, b3, or b4 is nonzero? Test using a = .05.

  2. Test H0: β1 = 0 against Ha: β1 < 0. Use α = .05.

  3. Test H0: β2 = 0 against Ha: β2 > 0. Use α = .05.

  4. Test H0: β3 = 0 against Ha: β3 ≠ 0. Use α = .05.

Question: Estimating repair and replacement costs of water pipes. Refer to the IHS Journal of Hydraulic Engineering (September, 2012) study of the repair and replacement of water pipes, Exercise 11.21 (p. 655). Recall that a team of civil engineers used regression analysis to model y = the ratio of repair to replacement cost of commercial pipe as a function of x = the diameter (in millimeters) of the pipe. Data for a sample of 13 different pipe sizes are reproduced in the accompanying table. In Exercise 11.21, you fit a straight-line model to the data. Now consider the quadratic model,E(y)=β0+β1x+β2x2. A Minitab printout of the analysis follows (next column).

  1. Give the least squares prediction equation relating ratio of repair to replacement cost (y) to pipe diameter (x).
  2. Conduct a global F-test for the model usingα=0.01. What do you conclude about overall model adequacy?
  3. Evaluate the adjusted coefficient of determination,Ra2, for the model.
  4. Give the null and alternative hypotheses for testing if the rate of increase of ratio (y) with diameter (x) is slower for larger pipe sizes.
  5. Carry out the test, part d, using α=0.01.
  6. Locate, on the printout, a 95% prediction interval for the ratio of repair to replacement cost for a pipe with a diameter of 240 millimeters. Interpret the result.

Minitab was used to fit the complete second-order modeE(y)=β0+β1x1+β2x2+β3x1x2+β4x12+β5x22to n = 39 data points. The printout is shown on the next page.

a. Is there sufficient evidence to indicate that at least one of the parameters—β1,β2,β3,β4, andβ1,β2,β3,β4—is nonzero? Test usingα=0.05.

b. TestH0:β4=0againstHa:β4≠0. Useα=0.01.

c. TestH0:β5=0againstHa:β5≠0. Useα=0.01.

d. Use graphs to explain the consequences of the tests in parts b and c.

Question: Ambiance of 5-star hotels. Although invisible and intangible, ambient conditions such as air quality , temperature , odor/aroma , music , noise level , and overall image may affect guests’ satisfaction with their stay at a hotel. A study in the Journal of Hospitality Marketing & Management (Vol. 24, 2015) was designed to assess the effect of each of these ambient factors on customer satisfaction with the hotel . Using a survey, researchers collected data for a sample of 422 guests at 5-star hotels. All variables were measured as an average of several 5-point questionnaire responses. The results of the multiple regression are summarized in the table on the next page.

  1. Write the equation of a first-order model for hotel image as a function of the six ambient conditions.
  2. Give a practical interpretation of each of the b-estimates shown.
  3. A 99% confidence interval for is (.350, .576). Give a practical interpretation of this result.
  4. Interpret the value of adjusted .
  5. Is there sufficient evidence that the overall model is statistically useful for predicting hotel image ? Test using a = .01.

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