1. Epidemiological Studies
Biomed I: Unit

2. Epidemiology is the study of disease incidence and its distribution in a population.
To prevent diseases we need to know how they are caused.
Epidemiologist try to determine how disease may be spread and which people get particular diseases by gathering data.
Epidemiology

3. Epidemiological studies
Divided into three general types:
1. experimental
2. descriptive
3. observational
Experimental: is the human equivalent of animal testing-providing or withholding a substance to determine its toxic or beneficial effects. Limited by ethical and legal considerations and number of participants.
Epidemiological studies

4. Eppidemiological Studies
2. Descriptive epidemiology analyzes data on the distributions and extent of health problems in various populations, trying to find correlations (two things that tend to happen together) among characteristics such as diet, air quality and occupation.
Eppidemiological Studies

5. Epidemiological Studies
3. Observational Epidemiology uses data derived from individuals or small groups to determine the strength between a particular variable and disease.
Epidemiological Studies

6. 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.
Examples

7. Epidemiological Studies
Early in this century, epidemiological studies established that the 14th century Black Plague was spread from rats to humans thru fleas.
In 1854, Dr. John Snow of London identified the source of a cholera outbreak to a contaminated water pump.
Epidemiological Studies

8. Epidemilogical Studies
In 1976, an outbreak of Legionnaires’ disease was traced to a bacterium that lived 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.
Epidemilogical Studies

9. Epidemiological Studies
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.
Epidemiological Studies

10. Strengths of Epidemiological Studies
These 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.
Strengths of Epidemiological Studies

11. Limitations to Epidemiological Studies
A 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 between a specific exposure and disease.
Limitations to Epidemiological Studies

12. There is difficulty in identifying control groups or “unexposed” populations, for example; the groups who can provide the data necessary for comparison.
Privacy must be considered
Can be quite expensive
Limitations con’t: