Thalles Mota, Leonardo Garcia, and Claudia Martins. 2026. Where Does Hardness Come From? An Instance Hardness Analysis of Substance-Use Prediction in Brazilian Adolescents. In Anais do XIV Symposium on Knowledge Discovery, Mining and Learning, outubro 19, 2026, Cuiabá/MT, Brasil. SBC, Porto Alegre, Brasil, 265-272. DOI: https://doi.org/10.5753/kdmile.2026.31988.