Bio-demographic information- your family background, what your parents do, information on your school and much more- helps the Admissions Committee form a picture of each applicant's context. Context refers to the unique opportunities, resources and challenges an applicant has had in his or her life. We look at a student's goals, interests and ambitions are and how a student has taken advantage of the resources available to him or her to achieve those goals or to explore those interests. Thus, context forms the framework by which we interpret the things we see in your application.
That said, the "Family" and "Demographics" sections of the Common Application are by no means the only place we gather contextual information; we look at school profiles which tell us what kind of curriculum a student’s school offers; we read the information students provide in the "Additional Information" section about any extenuating circumstances we should take into account; we take note of the listing of part-time jobs on an application. This kind of information helps us get an idea of your day-to-day life. Keeping what we know about your context in mind, we look at each student's interests and goals. We then ask whether, given the student's circumstances, he or she has gone above and beyond in pursuing academic, intellectual, personal, and/or extracurricular opportunities that have been available. We look for evidence that a student has pushed him or herself beyond his or her circumstances.
Following on this note, I would like to take this opportunity to debunk the myth that being from a particular background, socioeconomic class, racial group, etc. confers an advantage to an applicant - this is not true. Rather, it is how an applicant has met the unique opportunities and challenges in his or her life that make a student compelling in our applicant pool.