Many times it is not necessary to separate layers for each item, a short product stratification device can calculate the standard deviation and the standard deviation of the measured values ​​variation in product characteristics value variation, the product stratification method and computer program provide.
Products stratification device according to the present invention, based on a plurality of characteristic values ​​measured, stratifying the product in a predetermined plurality of ranks. The average value of the measured plurality of characteristic values, and calculates the standard deviation of the plurality of characteristic value variations as no standard deviation only each item. Among a plurality of predetermined rank stratified, remeasured several characteristic values ​​of the products belonging to at least one rank, based on a plurality of characteristic values ​​remeasured, the plurality of ranks given to each item of product re stratified, based on the probability distribution of the mean values ​​and considers the standard deviation for each item of the products that are calculated to estimate the estimated number of products in each rank when another at least once again layer for each item. Based on the estimated number, it calculates the measurement value dispersion of the product for each item.