Introduction to Epidemiology
Introduction to Epidemiology
What It Is
Contrary to popular belief, epidemiology is not the study of skin diseases—the root word is epidemic, not epidermis. The word epidemic itself comes from the Greek epi, meaning “among,” and demos, meaning “the people.” One scholar defined epidemiology as “the study of the distribution and determinants of health-related states and events in populations and the application of this study to the control of health problems.” .
For many years, if epidemiology was taught at all in medical schools , it was put in the same category as gross anatomy or biochemistry—one of those subjects you had to study but probably of no use in the real world. Fortunately, recent history is on our side. Before Legionnaires’ disease came along in 1976, the only people who had ever heard of epidemiology were other epidemiologists. Now that we have toxic shock syndrome (TSS), acquired immunodeficiency syndrome (AIDS), Agent Orange, repetitive strain injuries, the Gulf War syndrome, reactions to silicone breast implants, sick building syndrome, and leukemias purportedly caused high-tension wires, epidemiology is second on the list of careers advocated by every high school guidance counselor .
We still haven’t told you what epidemiology really is so we should get down to it. Alderson states that epidemiology includes four different types of studies: descriptive, hypothesis testing, interventional, and methodologic. Descriptive studies address questions like, “Who is most likely to develop AIDS?” or “What do the outbreaks of Legionnaires’ disease have in common?” or “Is there any association between kids who live near high-tension wires and the development of anemia?” This type of research (1) looks at the world as it is without trying to change it, (2) relies on existing data, such as the census, or (3) uses surveys of large groups of people to collect the information.
Once we have a good description of what’s related to what, we can ask more specific questions and move into the hypothesis testing phase. For example, if we suspect that the chances of developing breast cancer may be related to the intake of fatty foods, we can see if countries that have low-fat diets also have a low prevalence of cancer and if this prevalence is related to fat intake. Similarly, if we think that Legionnaires’ disease is caused by stagnant water in cooling systems, we can immediately test for water purity as soon as we hear about an outbreak. Again, we are pretty much leaving the world alone and “simply” gathering more focused information—information that can support or refute a specific hypothesis.
If after this stage our hypotheses are still viable , we may want to move on to the third stage, which is intervention studies. Now finally we’re getting a chance to change things. Rather than simply observing the relationship between low-density lipoprotein (LDL) cholesterol and coronary heart disease, we can do a study to see if lowering cholesterol in one group of people leads to a lower death rate than in people belonging to the group we leave alone. Notice that we’re still using hypothesis testing as with the second stage but with an added wrinkle—we now have more control over some of the variables.
Each of these types of epidemiologic research may require us to develop methods to gather the necessary data or carry out the intervention. For example, we were once interested in seeing if social support could ameliorate the adverse effects of stress on physical illness. To do so though we first had to develop an appropriate measure of social support because none of the existing ones met our needs. We also had to do a pilot study to determine the best way of ensuring compliance among the subjects completing health diaries (and returning them to us) during a 2-year span. These methods studies not only helped us carry out the major study but they also led to a number of publications.
Thus epidemiology covers a broad spectrum, overlapping with demography at one end, encompassing survey research in the middle, and looking much like experimental medicine at the other end. The common thread uniting all of these activities is a focus on groups of people rather than on individuals, molecules, cells, or mice.
Until relatively recently the field of epidemiology was more limited, covering only the first two aspects, descriptive studies and hypothesis testing. For this reason, studies of these types are sometimes called classical epidemiology or big-E epidemiology. Now the field includes clinical epidemiology, which got its start with the first modern clinical trial in the 1950s, although as we’ll see, studies of health effects of different regimens on humans can actually date their ancestry back 3500 years or so. Modern epidemiology incorporates both classical and clinical epidemiology. As Cassel noted, epidemiology is an example of a discipline that has expanded beyond its initial boundaries.
Content on this page was last changed on March 19, 2009.
© 2002 BC Decker Inc. Show Disclaimer
| 5476. | Streiner DL, Norman GR. PDQ Epidemiology. 2nd ed. Hamilton, Ontario: BC Decker Inc.; 1996. |
Next Page: Trends in Epidemiology »