The main goal of this course is to provide an overview of the scientific principles in clinical research. In the first part of the course, principles underlying all research designs are introduced. Topics covered include biological plausibility, the importance of comparison and temporality in establishing causality, data torturing, the formulation of a research question, refutation, placebo effects, and scientific conflicts of interest. In the second part of this course, three specific research designs are introduced: the case-control design, the cohort design, and the randomized controlled trial.