The contingency table shows results from the German study about whether there was an association between mobile phone use and eye cancer (Stang et al., 2001).
a. The study was retrospective. Explain what this means.
b. Explain what is meant by cases and controls in the headings of the table.
c. What proportion had used mobile phones, of those in the study who

(i) Had eye cancer

(ii) Did not have eye cancer?