A Pocket-Size Introduction -- The Big Picture - with Examples -- How to Set Things Up? Study Designs -- How Often does it Happen? Disease Frequency -- What's the Answer? Measures of Effect -- What is the Public Health Impact? -- Is There Something Wrong? Validity and Bias -- Were Subjects Chosen Badly? Selection Bias -- Are the Data Correct? Information Bias -- Other Factors Accounted for? Confounding and Interaction -- Confounding can be Confounding - Several Risk Factors -- Simple Analyses- 2́2 Tables are not that Simple -- Control - What It's all about -- How to Deal with Lots of Tables? Stratified Analysis -- Matching - Seems Easy, But not that Easy