5. A non-transitory computer readable storage medium storing instructions for determining exclusion efficiencies of a plurality of keywords appearing in a search result, the instructions comprising: calculating, for each of the plurality of keywords, an exclusion efficiency of the keyword if a search condition is applied to the search result and the keyword is applied as an exclusion keyword to the search result; indicating the exclusion efficiency of each of the plurality of keywords, wherein the calculating the exclusion efficiency of a keyword is based on a combination of a first parameter and a second parameter, the first parameter is a measure of a correlation between a subset of the search result satisfying the search condition and a subset of the search result excluded when the keyword is used as an exclusion keyword, and the second parameter is a measure of the search result excluded when the keyword is used as an exclusion keyword.
6. The computer readable storage medium according to claim 5 , wherein the exclusion efficiency of each of the plurality of keywords is a measure of the exclusion of unwanted data from the search result when the keyword is used as an exclusion keyword.