1. A computer system assisting document review performed by a user comprising; a processor; and a memory storing a document data; wherein the processor extracts a document group from the document data stored in the memory, the document group including a document to be reviewed by the user, receives result information issued to each document showing a result of review performed by the user, extracts one or more elements commonly appearing in each document in accordance with the issued result information respectively, where the element is morpheme included the document, calculates an evaluation value of each elements, where the evaluation value is a characteristic value indicating a dependency between the element and the result information corresponding to the document to which the result information has issued, calculates a score of the document based on the elements and—evaluation values of the elements, and calculates a recall ratio based on the score, the recall ratio defining reproducibility of the result of the review performed by the user where the reproducibility is an index indicating how well the computer automatically reproduces determination of the user, and the processor repeats the process until the recall ratio exceeds a unique target value.