Question

The following results were obtained in an environmental cohort study which was investigating the risk of brain cancer associated with exposure to high power transmission lines. Brain cancer was a binary variable meaning the person had it or did not.   

Radiation Dose (REM)	Total population	Cases of brain cancer	Cumulative Incidence	Relative Risk
0-0.99	25,000	2,700		1.0
1-4.99	10,000	1,300
≥5	2,000	1,500

Please fill in the table above. Please show all your work. Use the lowest radiation category (i.e. 0-0.99) as the referent group.

Please interpret the relative risk for the 1-4.99 and ≥5 REM groups compared to the referent group.

Based on the Bradford-Hill criteria discussed in the Causality lecture, what causal criteria is mainly demonstrated by this study? Provide your justification.

Answer 1

Relative risk of cases of brain cancer in radiation group (1-4.99) = incidence in radiation group 1-4.99÷ incidence in radiation group 0-0.99.

=1300/10000÷2700/25000

Relative risk=1.203

Relative risk in radiation group more than 5 = incidence in radiation group more than 5÷ incidence in radiation group 0-0.99

=1500/2000÷2700/25000

Relative risk =6.944

Bradford Hill proposed criteria to establish such an argument.one such criteria is strength of association.relative risk is the factor showing association of casuating factor to incidence. here in the study relative risk of 1.20 in radiation group (1-5) means that this group has 1.2 times more chance of getting brain cancer than reference group (ie. 0-0.99).

While relative risk of 6.944 in radiation greater than 5 group shows this group have 6.944 times more chance of getting brain cancer than reference group.

Hope this helps. All the best ?