A researcher wishes to investigate the relationship between risk factors and diabetes which is diagnosed is a h1ac blood tests is 6.5 of greater. she randomly selected 1000 medical records of individuals and divided them into two groups: group 1 had a family history of diabetes and group 2 did not. after following the groups for 5years, she finds that 34% of the group with a family history of diabetes has developed diabetes whereas only 18% of the group without a family history of diabetes has developed the disease what is the explanatory variable