31.With respect to testing the validity of the model’s results, Williams may wish to perform: A) a Durbin-Watson test, but not a Breusch-Pagan test. B) both a Durbin-Watson test and a Breusch-Pagan test. C) a Breusch-Pagan test, but not a Durbin-Watson test. D) neither a Durbin-Watson test nor a Breusch-Pagan test. The correct answer was B) Since this is not an autoregression a test for serial correlation is appropriate so the Durbin-Watson test would be used. The Breusch-Pagan test for heteroskedasticity would be a good idea. 32.Williams decides to use two-tailed tests on the individual variables, at a 5 percent level of significance, to determine whether electric generator sales are explained by each of them individually. Williams concludes that: A) all of the variables except snowfall explain sales. B) all of the variables except snowfall and housing starts explain sales. C) all of the variables explain sales. D) only low temperature explains sales. The correct answer was A) The calculated t–statistics are: · Heating Oil: (2.00 / 0.827) = 2.4184 · Low Temperature: (3.00 / 1.200) = 2.5000 · Snowfall: (10.00 / 4.833) = 2.0691 · Housing Starts: (5.00 / 2.333) = 2.1432 All of these values are outside the t–critical value (at (26 – 4 – 1) = 21 degrees of freedom) of 2.080, except the change in snowfall. So Williams fails to reject the null hypothesis for the other variables and continues to conclude that they explain sales, but rejects the null hypothesis with respect to snowfall and concludes that increases or decreases in snowfall do not explain sales. 33．When Williams ran the model, the computer said the R-squared is 0.233. She examines the other output and concludes that this is the: A) unadjusted R-squared value. B) the coefficient of correlation. C) adjusted R-squared value. D) neither the unadjusted nor adjusted R-squared value, nor the coefficient of correlation. The correct answer was C) This can be answered by recognizing that the unadjusted R-square is (335.2/941.6)=0.356. Thus, the reported value must be the adjusted R-squared. To verify this we see that the adjusted R-squared is: 1-((26-1)/(26-4-1))*(1-0.356) = 0.233. Note that whenever there is more than one independent variable, the adjusted R-squared will always be less than R-squared. 34．In preparing and using this model, Williams has relied on all of the following assumptions EXCEPT: A) there is a linear relationship between the independent variables. B) the disturbance or error term is normally distributed. C) the independent variables are uncorrelated with the residuals. D) a linear relationship exists between the dependent and independent variables. The correct answer was A) Multiple regression models assume that there is no linear relationship between two or more of the independent variables. The other answer choices are all assumptions of multiple regression. | 
发表于 2008-4-8 17:03
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