Randomly generated factors could be either qualitative or quantitative. For simplicity, qualitative factors had only two modalities, individuals having a 0.5 probability of being in each one. Quantitative factors were chosen for each individual randomly according to a standard normal distribution. To investigate how the nature of risk factors affects robustness, three scenarios were tested: i) all factors are qualitative; ii) all factors are quantitative and iii) half of the factors are quantitative while the other half are qualitative factors (mixed scenario).