This text deals with the design and accuracy of epidemiologic studies. It will give students a clear understanding of the research strategies used in experimental and non-experimental studies to ask the right questions, select the study population and follow-up period, obtain information on exposures, follow up disease occurrence, etc. Each step in the planning or critical evaluation of a study is illustrated by exercises based on actual studies. These exercises cover a wide range of exposures (including dietary factors, tobacco, alcohol, drugs, and radiation and occupational hazards) and diseases.