Variables:
A data frame with 8 observations on the following 7 variables.
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Experiment
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a factor with levels ObservedControl RandomizedControl
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Group
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a factor with levels Controls Grade2NotInoculated IncompleteVaccinations NotInoculated Placebo Vaccinated
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Population
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the size of the population in each group in each experiment
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Paralytic
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the number of cases of paralytic polio observed in that group
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NonParalytic
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the number of cases of paralytic polio observed in that group
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FalseReports
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the number of cases initially reported as polio, but later determined not to be polio in that group
Details
The data frame is in the form of a single table, but actually comprises the results of two separate field trials, given by Experiment. Each should be analyzed separately, because the designs differ markedly.
The original design (Experiment == "ObservedControl") called for vaccination of second-graders at selected schools in selected areas of the country (with the consent of the children's parents, of course). The Vaccinated second-graders formed the treatment group. The first and third-graders at the schools were not given the vaccination, and formed the Controls group.
In the second design (Experiment == "RandomizedControl") children were selected (again in various schools in various areas), all of whose parents consented to vaccination. The sample was randomly divided into treatment (Group == "Vaccinated"), given the real polio vaccination, and control groups (Group == "Placebo"), a placebo dose that looked just like the real vaccine. The experiment was also double blind: neither the parents of a child in the study nor the doctors treating the child knew which group the child belonged to.
In both experiments, NotInnoculated refers to children who did not participate in the experiment. IncompleteVaccinations refers to children who received one or two, but not all three administrations of the vaccine.
