1. A pattern verification method comprising: preparing a desired pattern and a mask pattern to form the desired pattern on a substrate; defining at least one evaluation point on an edge of the desired pattern; defining at least one process parameter to compute the transferred/formed pattern; defining a reference value and a variable range for each of the process parameters; computing a positional displacement for each first points on the transferred/formed pattern corresponding to the evaluation point, the first points computed using mask pattern and a plurality of combinations of parameter values obtained by varying the process parameters within the variable range or within the respective variable ranges, the positional displacement being displacement between first point and the evaluation point; computing a statistics of the positional displacements for each of the evaluation points; and outputting information to modify the mask pattern according to the statistics.