sas2 - 215 Lecture 21: MORE SAS Example: A sample of 10...

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215 Lecture 21: MORE SAS Example: A sample of 10 diesel trucks were run both hot and cold to estimate the difference in fuel economy. The results, in mi/gal, are presented in the following table. (From “in-sue Emissions from Heavy-Duty Diesel Vehicles,” J. Yanowitz, Ph.D. thesis, Colorado School of Mines, 2001.) _________________________ __ Truck Hot Cold 1 4.56 4.26 2 4.46 4.08 3 6.49 5.83 4 5.37 4.96 5 6.25 5.87 6 5.90 5.32 7 4.12 3.92 8 3.85 3.69 9 4.15 3.74 10 4.69 4.19 a) Can you conclude that the mean fuel mileage between hot and cold engines differ? b) Find a 98% confidence interval for the difference in mean fuel mileage between hot and cold engines. A SAS output based on this sample data is given below. options LS= 80 PS= 60 nodate; Data trucks; input hot cold; d=hot-cold; cards ; 4.56 4.26 4.46 4.08 6.49 5.83 5.37 4.96 6.25 5.87 5.9 5.32 4.12 3.92 3.85 3.69 4.15 3.74 4.69 4.19 ; proc ttest ; var d; run ;
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216 The SAS System The TTEST Procedure Statistics Lower CL Upper CL Lower CL Upper CL Variable N Mean Mean Mean Std Dev Std Dev Std Dev d 10 0.2865 ***** 0.5095 0.1072 0.1558 0.2845 Statistics Variable Std Err Minimum Maximum d 0.0493 0.16 0.66 T-Tests Variable DF t Value Pr > |t| d ** ****** *****
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217 Example: A researcher studied the effectiveness of two drugs (A and B) to relieve itching. Male volunteers aged 20-30 randomly received drug A or drug B intravenously, and then itching was induced on their forearms with cowage, an effective itch stimulus. The duration of the itching (in sec) for each subject is given below: Drug A: 161 218 211 173 242 157 105 197 223 192 Drug B: 199 143 113 197 176 144 87 120 A SAS output of this sample data is given below. data Drugs; input drug $ x; cards ; A 161 A 218 A 211 A 173 A 242 A 157 A 105
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218 A 197 A 223 A 192 B 199 B 143 B 113 B 197 B 176 B 144 B 87 B 120 ; PROC TTEST ; CLASS DRUG; VAR X; RUN ; The SAS System The TTEST Procedure Statistics Lower CL Upper CL Lower CL Upper CL Variable
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sas2 - 215 Lecture 21: MORE SAS Example: A sample of 10...

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