[Music] hello and welcome to epidemiology let me ask you a question what does risk mean to you what's a risky behavior if I start smoking what's my risk of getting lung cancer if you're a doctor and a patient asks you how do I ever decreasing heart disease by changing certain behaviors how you compute that how do you turn that into a a measurable concept well today we're going to talk about risk and how to measure risk you're going to learn how to set up a contingency table that's a kind of way that we use to display our numbers to compute risk it also learned how to calculate what we call relative risk and also how to calculate relative risk reduction and also you'll calculate absolute risk reduction all measurements of risk so analytical epidemiology is about discovering and describing relationships between risk factors and outcomes risk factors remember a risk factor is a independent variable that may change the probability of getting a certain outcome so we say that risk fat as smoking is a risk factor for lung cancer so sometimes we don't know if a behavior or a risk factor is causal or not we don't know if it actually causes an outcome the best we can say is that it's associated with an outcome smoking is associated with lung cancer we assume that it causes lung cancer it almost doesn't matter if it's causal or not we can control the outcome like by controlling the behavior or the risk factor so today we're going to explore what this association means if I say that this risk factor is associated with an outcome what do you think that means well it means that there is a statistical relationship between the exposure and the outcome we say that there is a numerical statistical relationship between whether or not you smoke and whether or not you get lung cancer [Music]