# Study Design ## Observational Studies Where we observe data from an existing phenomena or existence ## Experimental Studies We make changes to some parameters and study the output of a system or a phenomenon ## Observational Studies ### Ecological Studies entire population is considered as one unit. eg. smoking rate vs cancer rate ### Cross sectional studies - snapshot in time - survey results - prevalence ### Case control studies - Select people based on outcome (lung cancer people -> did you smoke) ### Cohort - select people based on factors (x component) - follow some smokers over time and see if they get cancer ### Randomized Controlled Trial - People are randomly assigned