FREQUENTLY ASKED QUESTIONS
General Questions

1. What is Science?
2. What is Biomedical Research?
3. What are Biomedical Research Methods?
4. What are Nonhuman Animal Models?
5. What is Clinical Research and What are Human Clinical Trials?
6. What are Epidemiological Studies?
7. What Difference has Biomedical Research Made to Human Health?

FAQ — The Care of Use of Animals in Biomedical Research (8-15)

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6. WHAT ARE EPIDEMIOLOGICAL STUDIES?
(Taken from Unit I, Chapter 3, of the Rx for Science Literacy teacher manual.)

Epidemiology is the study of disease incidence and its distribution in a population. To prevent diseases, we need to know how they are caused. By putting together data on which people get particular diseases and in which countries, epidemiologists try to determine how disease may be spread.

Epidemiological studies may be divided into three general types: experimental, descriptive and observational. Experimental epidemiology is the human equivalent of animal testing — providing or withholding a substance to determine its toxic or beneficial effects. Such studies are greatly limited by ethical and legal considerations as well as the difficulties involved in securing the cooperation of a large number of people.

Descriptive epidemiology analyzes data on the distribution and extent of health problems or other conditions in various populations, trying to find correlations among characteristics such as diet, air quality and occupation. Such comparisons are frequently made between countries and smaller geographic regions.

Observational epidemiology uses data derived from individuals or small groups. Data are evaluated statistically to determine the strength of association between a particular variable and disease. In cohort studies, a well-characterized and homogenous group is studied over time. In case-controlled studies, a control group is selected retrospectively based on variables thought to be relevant to the effort. Both methods rely on accurately predicting the important variables. They are subject to various selection biases.

This information gathering occurs “after the fact” and, as in the case of cancer, can occur many years after exposure. Thus, epidemiological studies do not demonstrate a direct cause and effect, but instead, establish a statistically significant association between exposure to causative factors and disease or ill-health effects.

Epidemiological studies have been in use for hundreds of years. Some examples are:

• In 1775, Sir Percival Pott of England reported that chimney sweeps had a very high incidence of scrotal cancer. His report may have been the first epidemiological study.
• Early in this century, epidemiological studies established that the 14th century Black Plague was spread from rats to humans via fleas.
• In 1854, Dr. John Snow of London identified the source of a cholera outbreak to a contaminated water pump.
• In 1976, an outbreak of Legionnaires’ Disease was traced to a bacterium that flourished in static water supplies such as in air conditioning units and was spread in tiny droplets. Effective cleansing and purification prevented further cases.
• Epidemiological studies have linked particular occupational settings such as asbestos plants and coal mines to various lung diseases.
• The Hammond-Horn Smoking Study (an analytic epidemiologic study undertaken by the American Cancer Society in 1952) decisively demonstrated the effect of cigarette smoking on death rates from cancer and other diseases.
  

Strengths: Epidemiological studies offer scientists a direct opportunity to study the effects in humans exposed to chemicals and disease-causing organisms.

These studies are also useful in identifying patterns in disease or injury distribution. These patterns may be traced to causative factors.

Limitations: A major disadvantage of epidemiological studies is that considerable human exposure can take place before a toxic effect is detectable, particularly in the case of diseases like cancer that take many years to develop.

It is also difficult to demonstrate a direct cause-and-effect relationship between a specific exposure and disease.

In addition, there are limited methodologies to measure or verify such things as an individual’s prior exposure, route of exposure or extent of exposure to a causative agent.

There is also difficulty in identifying control groups or “unexposed” populations, e.g., the groups who can provide the data necessary for comparison.

Privacy must also be considered, preventing the collection of additional data that would be useful to understanding the disease under study.

Epidemiological studies can also be quite expensive to conduct.

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