The school base weight for a sampled school is equal to the inverse of its probability of selection. The computation of the school base weight differs by whether the school was an originally selected school or a substitute school.
The school base weight for an originally selected school is equal to the inverse of its overall probability of selection. The school overall probability of selection is equal to the product of two quantities:
A school that takes the place of a refusing original school is known as a "substitute school". A substitute school is treated as if it were the original school that it replaced, and so is assigned the school base weight of the original school.