1. A screening method comprising the steps of: measuring respective electrical characteristic values of a plurality of semiconductor devices included in a wafer; acquiring respective positional information of the semiconductor devices over the wafer; subtracting components of variations in the electrical characteristic values depending on an on-wafer position of the semiconductor devices from respective electrical characteristic values of the semiconductor devices not depending on the on-wafer position of the semiconductor devices to thereby correct the respective electrical characteristic values of the semiconductor devices; generating distributions of the post-correction electrical characteristic values with respect to the semiconductor devices; and detecting semiconductor devices in which the post-correction electrical characteristic values assume outliers, out of the semiconductor devices, based on the distributions.