other cities? The following are data (ppb) on the ozone level obtained in
a forested area near Seattle, Washington:160 165 170 172 161
176 163 196 162 160
162 185 167 180 168
163 161 167 173 162
169 164 179 163 178
(a) Calculatex,s^2 , ands; compare the mean to that of Los Angeles.
(b)Calculate the coe‰cient of variation.2.21 The systolic blood pressures (in mmHg) of 12 women between the ages
of 20 and 35 were measured before and after administration of a newly
developed oral contraceptive (Table E2.21). Focus on the column of
di¤erences in the table; calculate the meanx, variances^2 , and standard
deviations.
TABLE E2.21Subject Before AfterAfter–Before
Di¤erence,di
1 122 127 5
2 126 128 2
3 132 140 8
4 120 119 1
5 142 145 3
6 130 130 0
7 142 148 6
8 137 135 2
9 128 129 1
10 132 137 5
11 128 128 0
12 129 133 42.22 A group of 12 hemophiliacs, all under 41 years of age at the time of HIV
seroconversion, were followed from primary AIDS diagnosis until death
(ideally, we should take as a starting point the time at which a person
contracts AIDS rather than the time at which the patient is diagnosed,
but this information is unavailable). Survival times (in months) from
diagnosis until death of these hemophiliacs were: 2, 3, 6, 6, 7, 10, 15, 15,
16, 27, 30, and 32. Calculate the mean, geometric mean, and median.
2.23 Suppose that we are interested in studying patients with systemic cancer
who subsequently develop a brain metastasis; our ultimate goal is to
prolong their lives by controlling the disease. A sample of 23 such
EXERCISES 99