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Observational and Interventional Epidemiology

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Another person whose name appears in the hall of epidemiological fame is James Lind.

He was a physician in the early 18th century, when scurvy was a major problem among sailors on long sea voyages. At that time, the cause of scurvy was not known. Bad air, congenital laziness and indigestible food were all suggested as possible causes. Lind observed that the sailors' diet was very poor, consisting of biscuits and salted fish or meat.

In 1747 he conducted an experiment at sea with 12 patients suffering from scurvy.


MCQ question here


Lind's experiment is an early example of interventional epidemiology (also known as experimental epidemiology). Lind divided his population into groups and allocated different treatments to each. Effectively Lind allocated a specific exposure (type of food supplement) to each group and then observed the outcome (whether or not scurvy improved).

What was particularly important was that he had comparison or "control" groups of patients who did not receive the intervention of interest, which meant that he could compare the outcome in those who received the intervention to those who did not.

Does Lind's experiment prove that oranges and lemons cure scurvy?

Write down some reasons for your answer before you answer the question.

More recently, the method of randomised trials was introduced, in which participants are randomly assigned to receive the intervention or an alternative, either a placebo or the standard treatment for the condition in question, which acts as a control.

Randomised controlled trials were first used in the 1950s - an early example was in the investigation the effect of streptomycin in the treatment of tuberculosis. This method has been increasingly used to evaluate new treatments and interventions since then.

We will discuss the role of chance in epidemiological studies in a future session, intervention studies in Chapter 17, and how to calculate sample sizes in the practical epidemiology study unit.

Aims and Objectives
What is Veterinary Epidemiology?
Snow on Cholera
Exposures & Outcomes
Observe or Intervene
Role of Epidemiology
Types of Investigation
A Clinical Problem
Population Perspective