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Minitab was used to fit the complete second-order modeE(y)=0+1x1+2x2+3x1x2+4x12+5x22to 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鈥1,2,3,4, and1,2,3,4鈥攊s nonzero? Test using=0.05.

b. TestH0:4=0againstHa:40. Use=0.01.

c. TestH0:5=0againstHa:50. Use=0.01.

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

Short Answer

Expert verified

a. At 95% significance level, it can be concluded 1=2=3=4=5=0.

b. At 99% significance level, it can be concluded that 4=0.

c. At 99% significance level, it can be concluded that 5=0.

d. A straight line can be drawn relating y to x1holding x2constant or the other way round.

Step by step solution

01

Goodness of fit

H0:1=2=3=4=5=0

Ha:at least one of the parameters 1, 2, 3,4 and5 are non-zero.

Here, F test statistic =SSEn-K+1=251.8134=7.406

H0is rejected if F 鈥 statistics < F0.05,34,34. For =0.05, since 7.406 > 1.843.

Not sufficient evidence to rejectH0 at 95% confidence interval.

Therefore,1=2=3=4=5=0

02

Significance of β4

H0:4=0Ha:40

Here, t-test statistic=^4s^4=-0.00430.0004=-10.75

Value oft0.005,34is 2.728

H0is rejected if t statistic > t0.005,34. For =0.01, since t <t0.05,199

Not sufficient evidence to rejectH0 at a 95% confidence interval.

Thus,4=0

03

Significance of β5

H0:5=0Ha:50

Here, t-test statistic=^5s^5=0.00200.0033=0.6060

Value oft0.05,34is 2.728

H0is rejected if t statistic > t0.005,34. For =0.01, since t <t0.005,34

Not sufficient evidence to reject at a 95% confidence interval.

So, 5=0.

04

Interpretation for second-order model

Since, the value of4=0and5=0at 99% confidence level, this means that the parabola does not have a curvature and it essentially is a straight line.

Here, a straight line can be drawn relating y toholdingx2constant or the other way round.

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