Question

1. In 1945, 1,000 women worked in a factory painting radium dials on watches. In 1975, the incidence of bone cancer in women who worked in the factory in 1945 was compared to the incidence of bone cancer in 1,000 women who worked as telephone operators in 1945. Twenty (20) of the factor workers and four (4) of the telephone operators developed bone cancer between 1945 and 1975. Calculate and interpret the risk ratio for developing bone cancer among radium exposed factory workers compared to telephone operators. Please show your work.

Answer 1

Risk Ratio / Relative Risk

It compares the risk of health events such as disease, injury or death among one group or the exposed group with the risk among the another group or the unexposed group. The ratio is calculated by dividing the incidence rate in an exposed group by the incidence rate in an unexposed group.

Group 1

Here the women who is working in the factory painting radium dials is directly exposed to Radium so can be coming under the exposed group.

Group 2

But women working as telephonic operators do not have direct exposure to radium so can be called as unexposed group.

For identifying the bone cancer after exposure to radium, the risk of bone cancer in each group is estimated from the cumulative incidence.Risk ratio can be obtained by dividing the cumulative incidence in exposed group by cumulative incidence in the unexposed group

Cumulative index can be calculated by, No of cases / Total number of population

Risk Ratio = Cumulative index in exposed group / Cumulative index in unexposed group

Type Of Work	Bone Cancer	No Bone Cancer	Total	Cumulative Incidence
Painting Radium Dials On Watches ( Exposed Group )	20	980	1000	20/1000 = 0.02%
Telaphone Operators ( Unexposed Group )	4	996	1000	4/1000 = 0.004%

Risk Ratio : 0.02/0.004 = 5

Cumulative incidence is an estimate of risk. A tottal of 1000 women worked in the factory painting radium dials on watches among them 20 developed Bone Cancer. So the cumulative incidence is 0.02%

We can similarly calculate the cumulative incidence among the 1000 women worked as telephone operators who did not exposed to radium, among them 4 developed Bone Cancer. So the cumulative incidence is 0.004%.

Interpretation

So the risk ratio here is 5. From this we can understand that women who is working in factory painting radium dials on watches & exposed to radium had 5 times the risk of development of Bone Cancer compared to the women who is working as a telephonic operators who is not exposed directly to radium.