6167SU07ans - STA 6167 Summer 2007 Exam#1 Name 1 Below are...

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STA 6167 Summer 2007 Exam #1 Name_______________________ 1. Below are edited SAS output for a simple linear regression application. The dependent variable is cost per passenger mile (CPM) in cents and the independent variable is the % of seats filled, also called the average load factor (ALF), of 33 airlines. Consider the measurements to be independent. S u m o f M e a n Source DF Squares Square F Value Model 1 1.527 1.527 5.034 Error 31 9.402 0.303 C Total 32 10.929 Root MSE 0.551 R-square 0.140 Dep Mean 3.106 Adj R-sq 0.112 C.V. 17.732 Parameter Standard T for H0: Variable DF Estimate Error Parameter=0 Prob > |T| INTERCEP 1 4.560 0.655 6.958 0.0001 ALF 1 -3.263 1.454 -2.244 0.0321 (7) a. Write a practical interpretation for the slope parameter estimate. Don’t simply say “slope of regression line.” State what the slope means in terms of CPM and ALF. 3.263 is an estimate of the expected decrease in CPM due to increasing ALF by one unit (1%). (7) b. Construct a 95% confidence interval for the slope of your regression line in 1.a. 3.263 +/- 2.0*1.454 (7) c. Do you think the intercept has any practical interpretation in this example? Justify your answer. Probably not. Mathematically, 4.560 would be an estimate of the expected CPM when ALF=0. But ALF=0 would mean no passengers. CPM ceases to have meaning for ALF close to 0; or even very low.
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(7) d. Set up a 95% confidence interval for the
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This note was uploaded on 01/22/2012 for the course STA 6167 taught by Professor Staff during the Fall '08 term at University of Florida.

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6167SU07ans - STA 6167 Summer 2007 Exam#1 Name 1 Below are...

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