1. A defect data analysis method comprising steps of: obtaining a distribution of defects based on defect position information obtained by inspecting a substrate with an inspection apparatus; and identifying the defect distribution as one of a plurality of distribution characteristic categories including at least a circular arc shaped regional defects category and classifying the defect distribution into an identified one of the distribution characteristic categories; wherein a step of identifying as the circular arc shaped regional defects includes sub-steps of: obtaining a center candidate point of the defect distribution of the circular arc shaped regional defects from the defect distribution based on defect position information obtained by inspecting a substrate using Cartesian coordinates; and extracting the circular arc shaped regional defects from corresponding polar coordinate information using the center candidate point as an origin.