1. A method comprising: (a) generating a set of samples, each sample representing a respective set of semiconductor fabrication process variation values; (b) selecting a first subset of the set of samples based on a probability of the set of semiconductor fabrication process variation values corresponding to each sample; (c) using a special purpose computer configured for estimating a yield measure for a semiconductor product based on relative sizes of the set of samples and the first subset, without performing a Monte Carlo simulation; and (d) outputting an indication that a design modification is appropriate, if the estimated yield measure is below a specification yield value.