A method includes: first identifying, from among one or more items included in a source code of a program, a first item used for storing data input to the program or data output by the program; associating, for each of predetermined ranges configuring the source code, an index value, based on a number of the first items referenced in the relevant predetermined range and the number of times the first item is referenced in the relevant predetermined range, with the relevant predetermined range; and outputting an association result of the index value for each of the predetermined ranges.