Abstract: Sales activity of a product at sales outlets including sales outlets at which sales activity data is sampled and unsampled sales outlets is estimated by determining the distances between each of the sampled sales outlets and each of the unsampled sales outlets and correlating sales activity data from the sampled sales outlets according to the determined distances. The sales activity volume of the product at the plurality of sampled outlets and the estimated sales activity volume of the product at the unsampled outlets are combined to obtain an estimate of sales activity for all the sales outlets. Sales activity of products prescribed by a physician at both the sampled and unsampled outlets can be estimated by correlating sales activity data for the prescribing physician at the sampled outlets according to the distances between the sampled outlets and the unsampled outlets.