HW2: [PG] Chapter 3, pages 59 - 64
     6, 7, 8, 9, 10, 14(a)

Exercise 6
a. The mean time to seizure is 25.9 months.
   The median is 24 months.
   The dataset has two modes: 12 months and 24 months.
   The range is 96-0.1 = 95.6 months
   The interquartile range is: 36-4=32 months.
   The sd = 27.5 months.
b. This is because sum of x_i's is equal to n times the average.

Exercise 7
a. The mean calcium level = 3.14 mmol/l.
   The median calcium level = 3.08 mmol/l.
   The standard deviation s = 0.51 mmol/l.
   The range = 3.84-3.27 = 1.47 mmol/l.

b. The mean albumin level is 40.4 g/l. The median is 42 g/l.
   The standard deviation is 3.0 g/l. The range is 9 g/l.

c. The patients suffering from vitamin D intoxication all have 
albumin levels within the normal range. However, they do not have
normal blood levels of calcium. Both the mean and the median lie
above the upper limit of the normal range; overall 6 of the 8 
patients have calcium levels that are above normal.

Exercise 8

a. For the bulimic adolescents, the median = 21.6 kcal/kg. 
   For the healthy adolescents, the median = 30 kcal/kg. 

b. For the bulimic adolescents, 
   the interquartile range = 25.2-18.1=7.1 kcal/kg. 
   For the healthy adolescents,
   the interquartile range = 36.6-23.8 = 12.8 kcal/kg. 

c. Daily caloric intake tends to be higher for the healthy adolescents. 
   This group also exhibits a greater amount of variability.

Exercise 9

Exercise 10

a. For smokers, the grouped mean serum cotinine level = 199.0 ng/ml,
             the grouped variance = 12,535.3 (ng/ml)^2,
             the grouped sd       = 112.0 ng/ml.
   For nonsmokers, the grouped mean serum cotinine level = 10.6 ng/ml,
             the grouped variance = 798.4 (ng/ml)^2,
             the grouped sd       = 28.3 ng/ml.

b. For smokers, the median serum cotinine level is the 769th measurement,
which falls in the interval 200-249 ng/ml. For nonsmokers, the median
is the 1722th measurement, which falls in the interval 0-13 ng/ml.

c. The mean and median serum cotinine levels are much higher in 
smokers than in nonsmokers. There is also a lot more varibility
in values among the smokers. 

Exercise 14

a. The grouped systolic blood pressure is 149.8 mm Hg. 
   The grouped variance is 373.45.  
   The grouped sd is 19.3 mm Hg.