 So let's look at the type of research. Now other than meta-analysis and systematic reviews, this is a good classification of medical research. And you see that two main classifies their observational studies and experimental research. Now in an observational study, we don't do anything special. That is just doctors or surgeons, we just go about our normal business, taking care of patients and we collect data on that and analyze that. That is as opposed to an experimental research where we say, whoa, stop the bus. We're going to design a study and we're going to alter our normal day-to-day routine. Now we usually talk about these as clinical trials or randomized trials where we're going to make groups of patients and we're going to select a random who falls into what group and every group will be managed differently. Whether we do different surgeries, whether we give different drugs, inclusive of a placebo drug, there's all sorts of experimental research in clinical medicine, but we intervene in an active way or even emit certain actions. That could also be done, but that's an experimental research, that's clinical trials or randomized trials. Observational trials, we're just going to gather data on our normal day-to-day business and you can well imagine what the strength and weaknesses of both of these main groups are. For the observational types of research, there's four main types. There's case series where you just take a set of patients and we just describe some variables in them. Then we get a case control series. That is really where we're going to compare two groups to each other. That is what this little study of ours is going to be about. We've got patients with a major and minor infection. That says case control, one can be the case, and the other one, the control. It doesn't really matter in this scenario that we have yet. It says that we have groups and we can compare them to each other. The specifics, though, of a case control series is that something happened and we look back in time. So in our little study, we have patients that already have either a minor or a major infection by definition and we looked at something before that. What is the CRP level? What is the HPA1C? That is opposed to the cohort study, which you see listed fourth on the list there. That is why we have a point in time and we look forward in time. Imagine we were to admit these two sets of patients, we treat them, and we look what happens over the subsequent days or weeks. So that is from a point looking forward. We'll also see these referred to as a prospect of cohort study. The third one that you see there, that's a cross-sectional study. It's very common. That's a prevalence type studies or it's just a flash point in time. It need not be an instant second. It might be over a week or over a month. These are usually prevalence studies if we're worried about epidemiology or if we hand out a survey for people to complete. These are cross-sectional studies, just a snapshot in time. So that is a good classification system to memorize and most studies will fall into either these groups or be some form of combination of these. Apart from these two main groups, of course, we get our systematic reviews and our meta-analyses. Our researcher is going to be a case-control series.