Randomized clinical trials: variants, randomization methods, analysis, ethical issues and regulations - Lazcano-Ponce, Eduardo; Salazar-Martínez, Eduardo; Gutiérrez-Castrellón, Pedro; Angeles-Llerenas, Angélica; Hernández-Garduño, Adolfo; Viramontes, José Luis (Salud pública de México, 2004)