1. A computer-implemented method for computing an estimated duplication rate of product listings in a product catalog, comprising: selecting a sample of product listings in a product category of the product catalog; identifying one or more product listings in the product category that are duplicates of product listings in the sample of product listings; computing a probability for at least a portion of the product listings in the sample and the duplicate product listings that the product listings would be included in a randomly selected sample of product listings in the product category; assigning a weight to the at least a portion of the product listings in the sample and to the duplicate product listings, the assigned weights being selected to reduce bias introduced by a location of duplicate product listings outside the sample of product listings, wherein the assigned weight for the at least portion of the product listings is inversely proportional to the computed probability for the at least a portion of the product listings; utilizing the weights assigned to the product listings in the sample and to the duplicate product listings to compute the estimated duplication rate of product listings in the product category, wherein the estimated duplication rate is based, at least in part, on dividing the weights assigned to the duplicate product listings by the weights assigned to the product listings in the sample and the weights assigned to the duplicate product listings; and utilizing the estimated duplication rate to reduce an actual rate of duplication of product listings in the product category of the product catalog.