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Question: Suppose you fit the interaction model y=0+1x1+2x2+3x1x2+ to n = 32 data points and obtain the following results:SSyy=479,SSE=21,^3=10, and s^3=4

a. Find R2and interpret its value.

b. Is the model adequate for predicting y? Test at =.05

c. Use a graph to explain the contribution of the x1 , x2 term to the model.

d. Is there evidence that x1and x2 interact? Test at =.05 .

Short Answer

Expert verified

a. The value of R2close to 95% indicates that almost 95% of the variation in the variables can be explained by the model.

b. At 95% confidence interval, it can be concluded that 1=2=3=0

c. Graph

d. At 95% confidence interval,3 . Hence it can be concluded with enough evidence that x1and x2interact in the model.

Step by step solution

01

Determining  R2

R2=1-SSESSyy=1-21479=0.95615

The value ofR2close to 95% indicates that almost 95% of the variation in the variables can be explained by the model.

02

Goodness of the model fit 

H0:1=2=3=0

Ha:At least one of the parameters 1,2,3 is non zero

Here, F test statistic =SSen-(k+1)=2132-4=0.75

Value of F0.05,28,28 is 1.915

H0is rejected if F statistic > F0.05,28,28. For =0.05, since F < F0.05,28,28

We do not have sufficient evidence to reject H0 at a 95% confidence interval.

Therefore, 1=2=3=0

03

Graph

When there鈥檚 an interaction term in the model, the model is estimated assuming one variable constant, and the relationship between the dependent and the other independent variable is plotted given the value of an independent variable.

In this case, two lines are plotted, where one line is drawn assuming x2 as constant K1 and the other line is drawn assuming x1 constant as t1 Since these two variables are interacting, it can be seen in the graph that the regression lines will interact at some point on the Cartesian graph.

04

Significance of  β3

H0:3=0

H0:30

Here, t-test statistic =^3s^3=104=2.5

Value of t0.05,31 is 1.6955

x1H0is rejected if statistic >t0.05,24,24. For, Since t > t0.05,31

Sufficient evidence to reject H0 at 95% confidence interval.

Therefore,34 . Hene it can be concluded with enough evidence that x1 and x2 interact in the model.

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