This manuscript is an introduction to the design and planning of clinical research. Practical issues are covered with a theoretical background. The refinement of a research question, searching and critically appraising the literature and management of references are discussed. Ethical concerns are raised throughout the development of the study protocol. Study designs are described and special emphasis is given to writing a protocol of a clinical trial. Sample selection and recruitment, variable measurement, randomization, follow up, statistical analysis, sample size and bias are covered. Tips...