1. A data analysis system for evaluating a relation between object data and a specified case, the system comprising a memory and a controller, wherein the memory at least temporarily stores the plurality of pieces of object data; wherein the controller: generates an index that enables ranking of a plurality of pieces of object data, the index being capable of being changed based on an input by a user; presents a reference data to the user; and permits the user to enter the input in order for the controller to rank the plurality of pieces of object data, wherein the ranking of the plurality of pieces of object data changes according to the index that changes based on the input, the input classifying the reference data which is different from the plurality of pieces of object data, on the basis of the relation between the reference data and the specified case; wherein the classification is executed according to a plurality of pieces of classification information according to the content of the reference data; and wherein at least one of the plurality of pieces of classification information is assigned to the reference data or the object data by the entry of the input; wherein the controller further: sets a combination of the at least one piece of the classification information, which is assigned to the presented reference data by means of the input by the user, and the reference data; extracts a pattern that characterizes the reference data from the reference data according to the classification information assigned by the input by evaluating a degree of contribution of each of a plurality of components contained in the reference data to the combination; sets the index for each of the plurality of the object data on the basis of the pattern; calculates a recall ratio based on the index of data for which the classification information is set; when the recall ratio is below a predetermined target value, repeatedly evaluates the degree of contribution of the plurality of components contained in the reference data and repeatedly extracts the pattern from the reference data, until the recall ratio reaches at least the predetermined target value; ranks the plurality of pieces of object data according to the index set on the basis of the pattern; and reports the plurality of pieces of ranked object data to the user.