A "secondary" Master's student is one who is getting a Master's or Ph.D. in another program while pursuing a Master's degree in Statistics. In the view of the Graduate School, the other department is your "primary" program, while Statistics is your "secondary" program. Secondary Master's students have a luxury that primary students in Statistics do not: They can begin taking courses just to see if the program fits into their plans without ever applying to become an official student of the program. Typically, an unofficial secondary Master's student will not apply to become an official student of Statistics until after completing the core. If the student wishes to earn the Master's under the Exam Option, then s/he may wait further until after passing the Master's Comprehensive Examination to apply to Statistics. In that case, letters of recommendation are not a necessary part of the application process. If the student wishes to earn a Master's degree under the Thesis Option, then letters of recommendation are required. One of these letters should be written by the Statistics professor who will be the thesis advisor.