1. A method, comprising: enumerating a list of all viewing combinations for a tuning event, for a number of people N at a location; determining a probability for each of the viewing combinations, using an independent probability of viewing for each of the N people at the location; determining a probability of a viewing condition using the probabilities of a first set of viewing combinations that have a first common characteristic, where the first set of viewing combinations is a subset of all of the viewing combinations.