# Study designs --- ## Ecological Studies - Measurements are in aggregates - Over space and over time - Example: - Fat in diet and breast cancer death rates - Measles vaccination and drop in Measles --- ## Fat in diet and breast cancer  --- ## Measles vaccination and Measles  --- ## Ecological Fallacy > What works in aggregated measurements does not work for individuals --- ## Case series - A number of cases closely studied - This study design is used for surveillance - Also for generation of hypotheses --- ## Disease Surveillance  --- ## Cross sectional study design  --- ## Case-Control Study  --- ## Cohort Study Design  --- ## Randomised controlled trial  --- ## Meta Analyses  --- ## Conclusion