Question with scenario A team of researchers set out to test a new medication developed to prevent the onset of diabetes in patients with a strong...

Question with scenario A team of researchers set out to test a new medication developed to prevent the onset of diabetes in patients with a strong family history of diabetes. They assembled a group of 200 patients and randomized them into two groups, one to receive a placebo and the other to receive the medication. They followed them each year for five years and ascertained the occurrence of diabetes using a glucose tolerance test. 

Could you help me pick out an independent and the dependent variable in this scenario and explain why? This is a prospective study. I am having trouble understanding the independent and dependent variables