Authors
Dr. DeWayne Derryberry
Idaho State University
Objective
Using data from a 1950’s study, determine whether the polio vaccine was effective in a cohort study, and, if it was, quantify the degree of effectiveness.
Background
In the 1950s polio was responsible for 6% of the deaths in 5- to 9-year-olds and left many more crippled. In 1954 a study was undertaken to determine the effectiveness of the Salk polio vaccine. The study was unusual in that almost 2 million first-, second- and third-graders participated in the study.
The study can be thought of in two parts:
- Randomized Experiment: In some areas of the country parents consented to have their second-grade children participate in a double-blind randomized trial. These children were randomly assigned to receive the vaccine or a salt solution (placebo) by injection.
- Cohort Study: In other areas of the country parents were less receptive to the notion of random assignment, and second-graders received the vaccine, while first- and third-graders were given nothing and treated as a control group.
When comparable groups are followed forward in time, the study is often called a cohort study. Both the randomized experiment and the cohort study began before the 1954 polio season and ended after the 1954 polio season.
See The Biggest Public Health Experiment Ever: The 1954 Field Trial of the Salk Poliomyelitis Vaccine, Paul Meier, http://www.stat.luc.edu/StatisticsfortheSciences/MeierPolio.htm.
The Task
Determine whether the vaccine was effective in the cohort study. And, if the vaccine was effective, quantify the degree of the effectiveness. We will leave a similar analysis of the randomized experiment as an exercise.