If tables are used in the guidelines those tables are computed by economists such as Policy Studies, Inc. They examine spending patterns of couples without children and couples with children in the consumer expenditure survey. The amount of additional money spent on the children (for expenses such as automobile insurance; AP exams; cell phones and plans; Christmas presents; educational expenses (trips, pictures, study guides, tutoring, AP and SAT exams, books, supplies, and uniforms); laptops; music lessons; parking fees; private school tuition; sports activities; and summer camps is computed and reduced to a table. Separating parents then find their incomes in the table and how much average intact families pay on children. In the widely used income shares model that amount is divided in proportion to the parents income.