Introductory Biostatistics

TABLE E4.18

Cases Controls

Duration of unprotected intercourse (years)

< 2 237 477

2–9 166 354

10–14 47 91

b 15 133 174

History of infertility

No 526 966

Yes

No drug use 76 124

Drug use 20 11

(a)For the first factor in Table E4.18, using ‘‘<2’’ as the baseline cal-

culate the odds ratio and its 95% confidence interval for each other

level of exposure.

(b)For the second factor, using ‘‘no history of infertility’’ as the base-

line, calculate the odds ratio and its 95% confidence interval for each

group with a history of infertility.

4.19 Consider the following measurements of forced expiratory volume
(liters) for 10 subjects taken from a study that examines the response to
ozone and sulfur dioxide among adolescents su¤ering from asthma:

f 3 : 50 ; 2 : 60 ; 2 : 75 ; 2 : 82 ; 4 : 05 ; 2 : 25 ; 2 : 68 ; 3 : 00 ; 4 : 02 ; 2 : 85 g

Calculate the 95% confidence interval for the (population) mean of

forced expiratory volume (liters).

4.20 The percentage of ideal body weight was determined for 18 randomly
selected insulin-dependent diabetics. The outcomes (%) were

107 119 99 114 120 104 124 88 114

116 101 121 152 125 100 114 95 117

Calculate the 95% confidence interval for the (population) mean of the

percentage of ideal body weight.

4.21 A study on birth weight provided the following data (in ounces) on 12
newborns:

f 112 ; 111 ; 107 ; 119 ; 92 ; 80 ; 81 ; 84 ; 118 ; 106 ; 103 ; 94 g

Calculate the 95% confidence interval for the (population) mean of the

birth weight.

180 ESTIMATION OF PARAMETERS