This report provides an introduction to epidemiology, including the definition and aims of the field. It discusses the main features of a cross-sectional survey and provides a description and justification of the study design. The report also compares and contrasts case-control and cohort study designs, and discusses the rationale for design selection. It explores the strengths and limitations of each design. Additionally, the report discusses the design and ethical issues in relation to a randomized controlled trial design and identifies a suitable alternative study design. Overall, the report provides a comprehensive overview of epidemiology and its various study designs.