• home

• content

  • introduction
    • what is epidemiology?
    • importance
  • descriptive epidemiology
    • collecting data
    • patterns and trends
  • analytical epidemiology
    • analyzing data
    • types of studies
  • applied epidemiology
    • strategies
    • control measures

• case studies

  • lung cancer
    • rpg
    • reality
  • smallpox
    • rpg
    • reality
  • food poisoning
    • rpg
    • reality

• interactive

  • games
  • interviews
  • survey
  • site test

• about

  • making of
    • Collaboration
    • Communication
    • Design
  • website
  • members
  • coaches

• sitemap

Analytical Epidemiology

Types of Studies

School children in Vietnam. Our team interviewed the epidemiologist who carried out a study of childhood poisoning in Vietnam
©Dr. Quan, 2007

There are many different kinds of epidemiological studies, and epidemiologists must choose the appropriate kind, according to the circumstances. If epidemiologists do not choose an appropriate study, they may have a hard time carrying out the study, and they may not end up with relevant data. Limited time and money are also factors that must be taken into account when choosing what kind of study to do. There are three common types of studies: cross-sectional, cohort, and case control.

Cross Sectional Studies:
Cross sectional studies are studies in which information about disease and exposure is collected from a non-specific population (participants are not specially selected according to specific conditions). It is basically the same thing as a survey.

• Advantages:
• Simple and inexpensive to perform - There is no need to go out and find people who meet a certain specification, and all that needs to be done is to ask the participant a few questions.
• Good at finding basic relationships between factors and disease.
• Disadvantages:
• The factors that the data shows to be related to the disease may not actually cause the disease; it may just be associated with the disease.

Case-control studies:
            In case-control studies, the participants in the study are selected according to whether they have the disease being studied or not. Information about exposures or other factors is collected separately from the two groups, and then compared to see if there are significant differences.

• Advantages:
• Detecting multiple factors that could have led to people developing the disease.
• Useful for studying rare diseases – this is because participants are selected by whether they have the disease or not. (Other types of studies may depend on a participant developing a disease, and this may not happen if the disease is rare.)
• Relatively quick, and inexpensive (although it requires slightly more time and resources than a cross-sectional study).
• Disadvantages:
• Hard to study rare exposures - If there was more than one factor that caused the disease, the participants with the disease in a study may not have been exposed to the rare factor. It could be likely that they could have been only exposed to a more common factor that could have caused the disease.

School children, buying sweets in front of a school in Hanoi, Vietnam. Due to the low hygiene, food poisoning is the main cause of childhood poisoning in Vietnam
©Dr. Quan, 2007

Cohort studies:
In a cohort study, the participants are selected according to past exposure to a specific factor. The participants are then followed forward in time (weeks to years, depending on the disease studied), to see if they develop the disease or not.

• Advantages:
• Detecting multiple diseases that are caused by a single exposure – this is because this type of study follows people forward in time, so all the effects of the single outcome are recorded.
• Studying the effects of rare exposures - because participants are selected according to if they have been exposed to a certain factor or not.
• Disadvantages:
• Requires a lot of resources. Cohort studies are expensive, and require a lot of time to conduct – this is because the patients may have to be monitored for a long amount of time.
• Requires many participants – this is to ensure that at least a few people in the study develop the disease, so accurate data can be collected.
• Hard to study rare diseases – this is because there could be a chance that none of the participants of the study will develop the disease if it is rare.

Sources:
“Introduction to Basic Epidemiology and Principles of Statistics for Tropical Diseases Control”. World Health Organization. 2002.

Okasha, Mona. "Epidemiological Research." Student BMJ (August 2001).

"An Introduction to Epidemiology." Centers for Disease Control and Prevention. .

"The Man Who Saved a Million Lives." The Observer 24 Apr. 2005. .

"Steps of an Outbreak Investigation." Centers for Disease Control and Prevention. .

Terms of Use | Credits | Acknowledgements 2006 – 2007 Disease Detective Team. All rights reserved.