9. A system configured to determine exclusion efficiencies of a plurality of keywords appearing in a search result, the system comprising: a processor that is configured to calculate, 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, and to indicate the exclusion efficiency of each of the plurality of keywords, wherein the processor is configured to calculate the exclusion efficiency of a keyword 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.
9. A system configured to determine exclusion efficiencies of a plurality of keywords appearing in a search result, the system comprising: a processor that is configured to calculate, 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, and to indicate the exclusion efficiency of each of the plurality of keywords, wherein the processor is configured to calculate the exclusion efficiency of a keyword 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. 12. The system according to claim 9 , wherein the exclusion efficiency of each of the plurality of keywords is indicated by displaying the exclusion efficiencies on a display device.