3. A case-control study was conducted to examine the association between pestici

Question

3. A case-control study was conducted to examine the association between pesticides and amyotrophic lateral sclerosis (ALS). A total of 5280 cases and 5280 controls were selected for inclusion in the study. Assuming that 4900 of those with ALS were exposed to pesticides and 784 of those without ALS were not exposed to pesticides, use this information to answer the following questions (32 total points).

Set up a 2 x 2 contingency table then calculate and interpret the appropriate measure of association (4 points).

Explanation / Answer

2 x 2 contingency table

ALS

Control

Exposed

4900

784

Unexposed

380

4496

Total

5280

5280

Since this is the case control study, therefore, Odds ratio is proper measure of association

Odd of exposure in the ALS group = 4900/380 = 12.8947368

Odds of exposure in the control group = 784/4496 = 0.1743772

Odds ratio = Odd of exposure in the ALS group/ Odds of exposure in the control group

=   12.89/0.17 = 73.94

Therefore, Odds ratio = 73.94

95% CI = 64.86 to 84.31, P = <0.0001

Results suggest that there is statistically significant association between pesticide exposure and ALS risk

ALS

Control

Exposed

4900

784

Unexposed

380

4496

Total

5280

5280

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