Folks, welcome back to Major Depression in the Population. This is Bill Eaton, and this is lecture three, in our presentation. And this lecture is called Basic Concepts of Epidemiology as Applied to Depression. And what I'm going to try to do for you, is teach you, that basic research designs, and concepts in epidemiology and to do this, I'm going to use examples from the area of depressive disorder. So you should learn something about epidemiology and something about depressive disorder. So the objective is, you should be able to understand and appreciate basic psychiatric epidemiologic research, and be able to criticize published research. That's our goal. So, the sections are. First section is epidemiology and the power of public health. Then there's a section for each of three research designs: ecological research, cohort research and case control study. And for each of those, I'm going to give you an example from the, the classical, you might say epidemiological literature, and then an example from literature, on depressive disorder. And then finally, we'll tackle something called the web of causation. So, here's Section A. What is Epidemiology? And, it's pretty simple, it's the study of diseases in populations. Now, we've talked about prevalence and incidence rates and so, there is a guy named Alex Langmuir who's defined epidemiology as the study of rates. And the thing is, these rates, they have a numerator, which is people with illness or disease, and a denominator, which is people in the general population. So you can see, the study of diseases in populations and the study of rates, is pretty much the same thing. There is a widely-used textbook by Lilienfeld and Stolley, that defines epidemiology as the study of occurrence of disease, by time, place, and person. And this gets more into the variation in rates, that you might find. And we will study that variation, in relation to depressive disorder. There's a little footnote there, a nota bene, that epidemiology is not the same as etiology, it's related, etiology is the study of causes of disease and we'll talk about how epidemiology contributes to that study, just now. So, there's a famous classic textbook by Jerry Morris called, Uses of Epidemiology, and if you only have one book to read in epidemiology, this is the one to read. I swear, you can have a glass of wine and read it after dinner, it's just so conversational and fun. And easy to follow, and it also has good knowledge of psychiatric issues in it, though it's not confined to that and these are the seven uses, you can see. The study of the history of health of populations. So, if you know the history of the health of a population in, Oklahoma or Burundi, you have some idea of what's going to happen to that population in the future. Another use is to diagnose the health of the community, and so that you can prioritize your health problems and we've already seen that in our study of Disability Adjusted life years, and dailies the burden of depression, showing that depression has a high burden in the population. Epidemiology let's you study the working of health services, so that you can learn how to improve them. Maybe too many in-patient services has happened in the 50s, not enough out-patient services and so forth. Four, you can estimate individual risks and you can talk about these risks for individuals. So you can tell an individual, you have a 6% chance of contracting a given disease, if you smoke, let's say, and a 2% chance if you do not smoke. And you can communicate that risk to individuals, and that can improve the health of the public. The fifth one, is to identify syndromes. Now, syndromes are collections of signs and symptoms of disease, and we talked about these signs and symptoms, with respect to depressive disorder, in our first lecture. But, it turns out, it's not obvious where the syndromes are. Sometimes a collection of signs and symptoms is obviously because of the way it occurs, in a cholera epidemic for example. It occurs suddenly and but for the mental disorders, the syndromes are harder to define because everything seems to happen more slowly and everything is a little bit more mushy. But epidemiology help us to identify syndromes, that are important. The sixth use identified by Morris is, to complete the clinical picture, of chronic disease especially and by this, he really means natural history. So, that is people with a depressive disorder now, what can we say about their future? And epidemiology can help us talk to that aspect, of depression. And then finally, to search for causes of health and disease and, and one of the ways that he talks about this, he says, to suggest clues to etiology. And a way that's the most interesting one. Epidemiology has a hard time proving anything, but it can be really helpful, in suggesting a cause and, that's one of the major benefits of epidemiology. Let me make the case for epidemiology here. This is a, a guy named Ernst Wynder, whose research I'm going to show you on smoking. One of the first guys to identify smoking as a possible cause of lung cancer. And he was a sort of a grand old man in 1992, and they asked him to write this review. And it has to do with the knowledge of prevention and etiology. The question is, do we learn how to prevent diseases, because we do bench science or work with rodents and discover some agent of disease and then apply it to the population? Or, do we basically, stumble on the way of preventing the disease, and later figure out what's causing what? It turns out that is almost always the case and that's what this table from Wynder's article shows you. So, for example, Lind discovered, that if you fed sailors limes, they would not get scurvy. And this is why you know, English people, the derogatory term for English people is sometimes called, they're sometimes called limeys. And you can see that Casal discovered how to prevent pellagra through good nutrition. But in 1755, a long time ago. But it wasn't till 1924, when Goldberger actually established the type of nutritional deficit that was related to pellagra. And so on down, you can see, Jenner discovered how to prevent smallpox through vaccination, but they basically had no idea what was going on, for another 200 years. So, likewise, Snow figured out how to prevent cholera, but it wasn't, in 1849, but it wasn't until 1893, when Koch discovered that it was the bacteria Vibrio Cholerae, that actually caused the disorder. So here's Epidemiology on the left and Bench Science on the right. And usually, epidemiology is in front, partly because people discover a clue to etiology in an epidemiology, or they just stumble on a possibility and try it out. And this is another demonstration of the same thing. This is a famous classical article by the McKinlays, in the Milbank Memorial Fund Quarterly and what it shows you is, on the X axis, you have time, and you have the rate of disease, various different rates of disease, on the Y axis, and you can see that in 1900, there was a high rate of measles and it went way down, by 1940. Now, some people might claim, look the measles disappeared because we learned how to vaccinate for it. But, that isn't apparently the case because the vaccine wasn't discovered until measles was practically eliminated. Same for Scarlet Fever, which penicillin was the, the curative agent, but it declined in prevalence, way down before penicillin was discovered. And so on, down to nine separate diseases. Even polio, whooping cough, flu and so forth and the upshot of this is that, preventive measures, mostly in the case of these diseases, just cleaning up the environment, separating the toilets from the water supply, and so forth. It has an enormously beneficial effect, and that effect is exercised in our historical perspective, basically, way before the curative agent is discovered. It's not to say that medicine isn't doing good work. It's just saying that, public health work historically, has been more important. So that ends the section, on what is epidemiology and why should we be working with it.
