The present invention provides a method of managing a stock replenishment system in a way that explicitly controls the in-stock rate. Also provided by the present invention is a method of managing a collection of stock replenishment systems in a way that the combined in-stock rate of the collection is controlled to a selected value. In addition, the present invention provides a method to set up a collection of stock replenishment systems in replenishment software systems in an identical fashion while controlling the combined in-stock rate. The methods of the present invention use point-of-sale data to determine packages-per-shopper rates, which are used as one of the inputs to statistical models of multiple-day retail sales.