Question

A hypothetical cohort study of pesticide exposure and cancer followed exposed pesticide workers and a comparison group of non-exposed employees of the same company over a 30-year period. Researchers found that the incidence of cancer among exposed workers was 55.3 per 1,000. In the comparison cohort not exposed to pesticides, the incidence of cancer was 15.7 per 1000. Calculate the relative and attributable risks of exposure to pesticides and development of cancer.

Answer 1

Solution:

Contingency table

	Total cases
Exposed	55.3 [a/(a+b)]
Unexposed	15.7 [c/(c+d)]

Step 1:

Calculate Relative Risk

Incidence of cancer among exposed workers = 55.3 per 1000

Incidence of cancer among unexposed workers = 15.7 per 1000

$RR =\frac{No.of exposed workers}{No.of unexposed workers}$

$RR = \frac{[a/(a+b)]}{[c/(c+d)]}$

$RR = \frac{55.3}{15.7}$

RR = 3.5222

The relative risk of development of cancer in exposed workers is 3.5 per 1000 workers.

Step 2:

Calculate attributable risk:

AR = No.of exposed workers - No.of unexposed workers

AR = [a/(a+b)] - [c/(c+d)]

AR = 55.3 - 15.7

AR = 39.6

The attributable risk of exposure to pesticides is 39.6 per 1000 workers.