4.6 Optional questions

These questions are optional; e.g., if you need more practice, or you are studying for the exam. (Answers appear in Sect. A.4.)

4.6.1 (Optional) Odds ratios

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. Pamphlett (2012) examined the association between the environmental exposure of toxins and sporadic motor neuron disease (SMND). A total of $380$ SMND cases and $377$ controls were studied. Of the $380$ SMND cases, $60$ had worked with metal in the past; of the $377$ controls, $33$ had worked with metal in the past.

What is the direction of this study?
Construct a two-way table showing the relationship between disease group, and whether not the specific person had worked with metal, in the sample.
Using your table, compute the odds that a person with SMND had worked with metal. Interpret what this means.
Using your table, compute the odds that a person without SMND had worked with metal. Interpret what this means.
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.)
Using your table, compute the percentage of people with SMND that had worked with metal.
Using your table, compute the percentage of people without SMND that had worked with metal.
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?
Sketch a bar chart to display the data.

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.