1. A method for scaling a panel of users with known attributes to determine an unknown attribute of a user, the method comprising: receiving, by one or more computers, an unclassified attribute vector of the user, the unclassified attribute vector comprising first attributes and first attribute values; producing, by the one or more computers, a reduced attribute vector using the unclassified attribute vector and a projection matrix, wherein the reduced attribute vector has fewer attributes than the unclassified attribute vectors; producing, by the one or more computers, a plurality of reduced panel attribute vectors using a plurality of classified panel attribute vectors of users from the panel and the projection matrix, wherein the reduced panel attribute vectors have fewer attributes than the classified panel attribute vectors, and wherein the user is not one of the users from the panel; and determining, by the one or more computers, the unknown attribute of the user based on the reduced attribute vector, the plurality of reduced panel attribute vectors, and the known attributes, wherein each of the known attributes corresponds to a different reduced panel attribute vector.