A study in China assessed the association between eating American brown rice and type 2 diabetes by administering food frequency questionnaires to a study population of students at Wuhan University. Questionnaire results showed that 5,000 students ate American brown rice at least 5 times per week (highest exposure group), while 1,000 students ate American brown rice less than once per month (lowest exposure group). None of the students had diabetes at the start of the study. By the end of the study, 100 of the students from the highest exposure group had developed diabetes, while 300 of the students from the lowest exposure group had developed diabetes.

1. What is the study design?
2. Construct a 2 x 2 contingency table demonstrating the relationship between American brown rice consumption and diabetes.
3. Identify and calculate the best relative measure of association, and interpret the results.