Introductory Biostatistics

ad

n

¼

ð 11 Þð 203 Þ

299

¼ 7 : 47

bc

n

¼

ð 35 Þð 50 Þ

299

¼ 5 : 85

The process is repeated for each of the other two smoking levels. For moderate
smokers

ad

n

¼

ð 70 Þð 220 Þ

549

¼ 28 : 05

bc

n

¼

ð 42 Þð 217 Þ

549

¼ 16 : 60

and for heavy smokers

ad

n

¼

ð 14 Þð 50 Þ

163

¼ 4 : 29

bc

n

¼

ð 3 Þð 96 Þ

163

¼ 1 : 77

TABLE 1.18

Smoking Shipbuilding Cases Controls

No Yes 11 35
No 50 203
Moderate Yes 70 42
No 217 220
Heavy Yes 14 3
No 96 50

TABLE 1.19

Shipbuilding Cases Controls Total

Yes 11 (a)35(b)46ðr 1 Þ
No 50 (c) 203 (d) 253 ðr 2 Þ

Total 61 ðc 1 Þ 238 ðc 2 Þ 299 ðnÞ

28 DESCRIPTIVE METHODS FOR CATEGORICAL DATA