A method of calculating a probability of failures caused only by defects, a method of calculating a defect limited yield using the classification of pattern parameters extracted only from the defects, and a system for calculating the probability of failure and the defect limited yield are provided. In one exemplary embodiment for calculating a probability of failures caused only by defects, defects are detected in inspected blocks that have defects and in blocks located around the inspected blocks to measure the number of inspected blocks that have failures caused by reasons other than the defects in the blocks located around the inspected blocks having defects (n1), the number of inspected blocks having no failures in the blocks located around the inspected blocks having the defects (n2), the number of inspected blocks having failures caused by defects in the inspected blocks having defects (n3), and the number of inspected blocks having no failures in the inspected blocks having defects (n4). The data (n1) through (n4) is then substituted in the following formula: ##EQU1##

where ##EQU2##

and ##EQU3##