Basic Applied Statistics 200
Solutions to Practice Midterm 1 Fall 2002

1.  
   1. (i) Method 1 because the values tend to be lower
   2. (iii) both about the same
   3. (i) Method 2 looks somewhat left-skewed (long left tail)
   4. (iv) neither has values far from the rest
   5. (ii) mean and standard deviation because it is fairly symmetric, but you could make a case for the 5 Number Summary because there is (slight) skewness
   6. 13, 19 (3rd value), 24, 28 (8th value), 31
   7. neither (this should have been included as an option)
2.  
   1. 0 is the mean of a standard normal distribution
   2. 1 is the standard deviation of standard normal z
   3. .1003 are GREATER (.8997 would be less)
   4. practically no observations are this high
   5. .9772-.8413=.1359
   6. look up .0404; the closest z is -1.75
   7. look up .9900 (because you want the HIGHEST 1%); the closest z is 2.33
3.  
   1. 95% are within 2 s.d.s of the mean: 5.3 plus or minus 2(.2) goes from 4.9 to 5.7
   2. z=(4.8-5.3)/.2=-2.5; the proportion below is .0062
   3. no, not likely because the probability .0062 is so small
   4. for .25 below, z=-.67, so x=5.3-.67(.2)=5.166
4.  
   1. men who died (3160/2223) have the highest proportion
   2. 332/706=.47
   3. 332/1692=.20
   4. 374/531=.704
5.  
   1. tip
   2. (i) increase (points slope up)
   3. (iii) rather strong (points are fairly tightly clustered)
   4. (v) +.83 because the relationship is fairly strong, but you could take the square root of R-Sq=.686 to be sure
   5. (ii) same; r is independent of assignment of explanatory/response
   6. -.35+.15(63.30)=9.19
   7. 12-9.19=2.81
   8. (iii) it predicts 15% of the bill minus 35 cents (see regression equation)
   9. (i) random scatter is a good thing in the residual plot
   10. (ii) decrease because it would make the clustering looser
6.  
   1. (iii) not enough replication; 5 each are small groups
   2. (i) no comparison is made
   3. (ii) no randomization; people chose what medication to take
7.  
   1. 25 is the number actually examined
   2. observational study; the pediatrician does not manipulate any variables, she only observes

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