The Keyword Efficiency Index is a weighted quotient of the keyword and the search phrase. It is about the ratio between the number of times a keyword is entered into a search engine, (How often is the keyword entered?) and the number of search results. The latter reflects the potential competitors.
The quotient becomes more favorable the more often a search word is entered and the lower the number of search results. The lower the KEI index is, the more interesting the search term is and the higher the chances of appearing far in front in the results pages.
Assuming that the number of search queries for a keyword is 1,230 and the number of search results is 446,612, the KEI index is calculated from the ratio of 446,612 to 1,230. The KEI index is therefore 363.