Descriptive Studies – Epidemiology and Biostatistics

00:02 Sometimes when people say the epidemiology of a disease, what they actually mean is the description of that disease and that brings us to talking about descriptive epidemiology or descriptive study, by the way, I don't like it when we say the epidemiology of a disease, it's a limiting description of the full breath and majesty and complexity of what the science of epidemiology brings to the table. But when they say descriptive epidemiology, what we are talking about is the who, who gets a disease or an outcome, the what, what is that they're getting, the where, where is it happening and when, when is it happening.

00:37 Notice that there is no why there, there is just four W's, who, what, where and when.

00:44 When we're into the why, we're into a deeper kind of investigation. Descriptive epidemiology only cares about describing the who, what, where and when. So let's think of an example.

00:55 Let's decide that we're going to investigate the prevalence of left-handedness among students in your neighborhood. Who are we dealing with? Students. What? Left-handedness. Where? The place where you live, your neighborhood. And when? Right now, we care about measuring this prevalence, this distribution right now and so the thing that I'm measuring, the thing that I'm ascertaining is right now 23% of students in your neighborhood are left-handed.

01:22 That's a very simple and relatively useless observation, but a good description of descriptive epidemiology.

01:31 Now I want to talk a bit about the way the study designs or taxonomise, how we categorize them. Because a large part of epidemiology is in designing studies to acquire the evidence that fits within our research paradigm. So the first large delineation I want to draw attention to is qualitative versus quantitative studies. In qualitative research, that's the world of social sciences, the world of clinical science and sometimes health sciences, that's when we're dealing with descriptions that are qualitative, words, themes, things like that. Quantitative research is numbers, statistics and that's where we're going to live, we're going to live in the world of quantitative research in epidemiology. Amongst quantitative studies we have descriptive versus analytical studies. Bow descriptive studies we've talked about already, that's the who, what, where and when. And one example of a descriptive study is a cross-sectional study, which we will describe in greater depth later. I just did an example, left handedness in my neighborhood, that's a cross-sectional description of a particular phenomenon. When we are looking at two different variables or more variables and how they relate to one another, then we're into the world of analysis, into analytical studies. Now descriptive studies dealt with one variable really, describing left-handedness.

02:56 Analytical studies are looking at two variables or more and a relationship between them. Amongst analytical studies, there are two other categories, observational or experimental. Amongst observational studies, there are three perhaps four, large categories; the case control, the cohort, the different kinds of cross-sectional studies and possibly this thing called ecological study, all of which we learn more about in another lecture. The distinguishing characteristic of observational studies is that we observe them, the universe unfolds and we observe.

03:33 We don't determine who does what or who gets what, all we do is we watch and we marvel in the way that the universe unfolds. Experiments on the other hand, that's when we do get to interfere a bit. The classical experiment in epidemiology is the randomized controlled trial or the RCT, also called clinical trials. There are other kinds of experiments as well, there are quasi-experimental designs, there are natural experiments and we will talk about more of those in a future lecture as well. Now when the lay person thinks about an experiment, they mean any kind of study, any kind of investigation. When epidemiologists talk about an experiment, we mean something very particular, we're talking about when we manipulate a variable. So perhaps we are deciding who gets a drug versus who gets a placebo, or who gets to smoke versus who doesn't smoke. Whenever we are telling people what to do, we are conducting an experiment.

04:30 We manipulate something, we manipulate a variable. In observational studies we don't, we let the universe unfold as it would. We let people choose what they are going to do. We may select them, based upon what they're doing, but we don't tell them what to do. An experiment involves us changing a variable.

04:46 Well now that we've covered the differences between analytical and descriptive studies and the differences between observational and experiment studies, let's look at some historical examples. In particular, I want to talk about the triumphs of epidemiology, one in particular