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Introduction to observational studies

Learning outcomes

On watching this video students should be able to:

  1. List different types of observational study.
  2. Discuss the hierarchy of evidence tool.
  3. Explain why an observational study can generally only be used to describe associations rather than causation, and put them into the context of the hierarchy of evidence.
  4. Discuss why not all research questions can be investigated using an experiment and identify examples and describe why?


Black N. 1996. Why we need observational studies to evaluate the effectiveness of health care. BMJ

Kallen B. 2012. The problem of confounding in studies of the effect of maternal drug use on pregnancy outcome. Obstetrics & Gynecology.

Epidemiologists now feared to have spread worldwide

New York – A new report by the World Health Organization has confirmed fears that epidemiologists have now spread worldwide.

“We always thought this might happen, but we never suspected it would happen so quickly”, said spokesperson for the WHO, Dr. Sue Yu.

“The correlation between the increase in the number of epidemiologists and the increase in the number and kinds of illnesses is striking and cannot be ignored”.

“Countries that didn’t have any epidemiologists until recently also didn’t have diseases like Autism or heart disease or many illnesses until their countries were infected with epidemiologists”.

“North Korea, for instance, has no epidemiologists and no disease.  I repeat, NO disease”.

“This cannot be mere co-incidence”.

“Today we stand firm with the people of these countries that have seen a recent surge in epidemiologists and we appeal to them to do something about the epidemiologist plague that has infested their countries.  We also appeal to US president Barack Obama to pledge support for these countries in their efforts to get us back to where we were in the 1970s with few epidemiologists and much much fewer diagnoses of illness”.