1. A processor-based method for determining difficulty measures for training cases used in developing a solution to a problem, comprising: providing a set of training cases having respectively associated difficulty measures; operating a candidate solution on a particular training case; determining a performance measure of the candidate solution operating on the selected training case; determining a credibility rating of the candidate solution, the credibility rating indicating a proficiency level of the candidate solution at solving training cases; and modifying the difficulty measure of the particular training case based on the performance measure of the candidate solution operating on particular training case and the credibility rating of the candidate solution.