In some embodiments, the appearance of a line corresponding to correlations between attributes does not become different according to the result of right or wrong solution in a unit of problem. The right or wrong solution can be determined in a unit of correlation between attributes. For example, in a case that a user selects an answer identified when he or she does not correctly understand correlation between specific attributes, his or her selection may be found to be wrong solution with respect to the correlation between the specific attributes, but it may be found to be right solution with respect to correlation between different attributes in the same problem. For example, with reference to FIG. 14, the correlation between the first and second attributes may be found to be right solution, and the correlation between the second and third attributes may be found to be wrong solution, in the second problem. Through this, a precise analysis to a learner becomes possible.

Specifically, with reference to FIG. 15, the characteristic of problem set analyzed according to the method for indicating characteristic of problem set according to the above-described fifth embodiment of the present invention is depicted. According to this, strong or weak points of a learner can be easily distinguished from each other, through the color of lines indicating correlation between attributes.