You will examine a good design for a medical experiment. Note the quantity of new vocabulary in this lesson. The text examines the key elements in a randomized, controlled, double-blind experiment, and explains why each is necessary. The primary example is the Salk vaccine field trial. We compare polio rates for children who were vaccinated against those who were deliberately not vaccinated and those who refused treatment.
Randomization is necessary to prevent selection bias .
Selection bias results when the treatment and control groups are different because people are assigned to them differently, based on other factors. These factors can be confounded with the treatment, making interpretation of the experimental results difficult. It is best to assign subjects to the different groups randomly. Control groups are necessary so we can compare the results of the treatment group against a similar group to see if the treatment makes a difference. Historical controls are sometimes used, but they can result in biases if the historical group is different from the treatment groups.