A data analysis method for an integrated circuit process is described, for analyzing the results of at least an in-line quality test, a product test and a yield test done to the products of the IC process. The products are divided into a normal group and an abnormal group based on the result of the in-line quality test, and are divided into a qualified group and an unqualified group based on the result of the yield test. A categorization step is performed to define the intersection of the unqualified group and the normal group as a first problematic group and to define the intersection of the unqualified group and the abnormal group as a second problematic group. By analyzing one or both of the two problematic groups, the major yield killer can be identified so that process modification can be made accordingly to improve the yield.