<qa>  What is the primary goal of a double blind study design?Current literature suggests that 25-hydroxyvitamin D 25OHD is inversely related to risk of type 2 diabetes mellitus T2DM. African Americans AA have significantly less 25OHD concentrations, greater chances of poor glycemic control compared to European Americans EA. The primary objective is to evaluate if the differences in glycemic control in children with type 2 diabetes are explained by differences in serum concentrations of 25OHD. A secondary aim is to demonstrate that subjects with vitamin D deficiency serum 25OHD 20ngml and T2DM who receive an 8 week of vitamin D treatment 50,000 IU oral vitamin D2once per week have greater improvement than subjects who receive placebo in glycemic control, as measured by HbA1c and endogenous insulin secretion, as assessed by area under the concentration-time curve AUC for mixed meal-stimulated C peptide, at 3 months after study drug administration. Research design: Randomized, placebo-controlled, double blind study design in children with T2DM and vitamin D deficiency. Glycemic control will be determined by HbA1C levels, fasting glucose and area under the curve AUC for glucose after a mixed meal tolerance test MMTT. Measures of beta cell function will be determined by AUC for c-peptide and glucose after MMTT. This study is warranted in AA adolescents with T2DM as any positive interventions could have life long impact and will lead to future larger clinical trials. 