1. A method of determining a reliability indicator for at least one set of signatures determined from clinical data collected from a group of samples, the signatures being obtained by detecting characteristics in the clinical data from the group of samples, where each of the signatures generate a first set of stratification values that stratify the group of samples, the method comprising: providing at least one additional stratification source to the signatures obtained from said group of samples, wherein the at least one additional stratification source is independent from the signatures and generates a second set of stratification values for the group of samples, comparing, by a processing system, the first set of stratification values with true reference stratification values to provide a first set of similarity measure indicators for each signature, comparing, by the processing system, the second stratification values with true reference stratification values to provide a second set of similarity measure indicators, and determining, by the processing system, the reliability of the signatures based on at least one of: differences between the first and second set of similarity measure indicators, and matches between the first and second set of similarity measure indicators.