Building on articles previously published in The Lancet, this handbook is essential for busy clinicians and active researchers interested in research methods in epidemiology. The needs of clinicians predominate throughout the text, but these needs overlap with those of researchers especially in chapters covering randomized controlled trials. For readers to assess trials accurately they need to understand relevant guidelines on the conduct of trials that are emerging from methodological research. ..In presenting these discussions to clinicians these chapters will help researchers who also do randomized trials and provide a methodological background that enhances the quality and quantity of their research productivity.Enables clinicians to read the medical literature more criticallyChapters cover: descriptive studies, cohort studies, case control studies, bias, and screening testsFive chapters dedicated to randomized controlled trials