## 4.11Optional: Odds ratios

This question is optional; for example, if you need more practice, or you are studying for the exam.

(Answers are available in Sect. A.5)

This question has a video solution in the online book, so you can hear and see the solution.

The impact of environmental toxins is not well understood. A 2012 Australian observational study examined the association between the environmental exposure of toxins and sporadic motor neuron disease (SMND).

A total of 380 SMND cases were studied, and 377 controls. Of the 380 SMND cases, 60 had worked with metal; of the 377 controls, 33 had worked with metal.

1. Construct a two-way table showing the relationship between disease group, and whether not the specific person had worked with metal, in the sample.

2. Using your table, compute the odds that a person with SMND had worked with metal. Interpret what this means.

3. Using your table, compute the odds that a person without SMND had worked with metal. Interpret what this means.

4. How many times greater is the odds that a person with SMND having worked with metal, compared to the odds that a person without SMND having worked with metal? (This is an odds ratio.)

5. Using your table, compute the percentage of people with SMND that had worked with metal.

6. Using your table, compute the percentage of people without SMND that had worked with metal.

7. A newspaper report states SMND rates are almost the same between those worked with metal and those who did not.

Do you agree or disagree?

### References

Pamphlett R. Exposure to environmental toxins and the risk of sporadic motor neuron disease: An expanded Australian case–control study. European Journal of Neurology. 2012;19:1343–8.