Two indices are presented for each occupational group. 
The smoking index is the ratio of the average number of 
cigarettes smoked per day by men in the particular 
occupational group to the average number of cigarettes 
smoked per day by all men. The mortality index is the 
ratio of the rate of deaths from lung cancer among men in 
the particular occupational group to the rate of deaths 
from lung cancer among all men. 

Each observation consists of the following variables:

a) Occupational Group 
b) Smoking index - 100 = average
c) Lung cancer mortality index - 100 = average

In this case consider mortality index to be the dependent 
variable and smoking index the independent variable.