Population Research Designs – Observational Studies (Study Designs)

00:01 Hello and welcome back to epidemiology. In today's lecture we're going to get into the meat and potatoes of population epidemiology, that is the design of observational studies, so much of my personal consulting work involves advising people on how to design studies and how to critique their existing designs, so I think you'll find this quite interesting.

00:22 After today's lecture, you'll be familiar with the main observational study designs, it's not an exhaustive list, but we get to the main ones. You will also know the difference between prospective and retrospective designs and you’ll know why sometimes, we like to match subjects across study designs and study groups. You'll also know why some designs are more appropriate than others and that I want for you to be able to do is to be able to tell when to use certain designs in what contexts.

00:51 So first let's go over how our various designs splay across the research universe.

00:57 You'll recall that we tend to have either qualitative or quantitative research. Qualitative is what the social scientists tend to do and quantitative involves numbers and statistics. Amongst quantitative designs we have descriptive or analytical approaches. Under descriptive we are describing a scenario or a sample, who gets the disease, when do they get it, where do they get it, who, what, where, when essentially. But the analytical approach involves an association between two or more variables and we either have an observational scenario or an experimental scenario. The difference is that in experiments you the investigator are manipulating a variable, are causing a group of subjects to have an experience that they otherwise would not have had, whereas the observational scenario you're letting the universe unfold as it will and you're just observing. Amongst the observational designs, we have the case control, the cohort and cross-sectional and that's what we're going to talk about in this lecture. The experimental approaches tend to be intervention, clinical trials, RCTs and so forth. So again today, we are focusing on the observational designs, the case control, the cohort and the cross-sectional.

02:10 Now how do we rank these various designs, in the sense of most difficult to least difficult? Well the least difficult is probably the cross-sectional design, a survey is cross-sectional, that's when I want to know what's happening right now. Next up is the cohort study, it's expensive and difficult, but it's intuitive and easily understood. The case control is next, it's not as intuitive and a little less expensive, but is not easy to do. Lastly the experiment is always the most difficult, the most expensive and we tend to reserve that for things we really care about.

02:46 So we're going to work through a particular scenario and that scenario is the question, is there an association between smoking and lung cancer. Smoking is our risk factor, our exposure, lung cancer is the outcome that we care about. Now let's talk about how we