The data frame PolioTrials gives the results of the 1954 field trials
to test the Salk polio vaccine (named for the developer, Jonas Salk),
conducted by the National Foundation for Infantile Paralysis (NFIP). It is
adapted from data in the article by Francis et al. (1955). There were
actually two clinical trials, corresponding to two statistical designs
(Experiment), discussed by Brownlee (1955). The comparison of
designs and results represented a milestone in the development of randomized
clinical trials.
A data frame with 8 observations on the following 6 variables.
Experimenta factor with levels ObservedControl RandomizedControl
Groupa factor with levels Controls Grade2NotInoculated IncompleteVaccinations NotInoculated Placebo
Vaccinated
Populationthe size of the population in each group in each experiment
Paralyticthe number of cases of paralytic polio observed in that group
NonParalyticthe number of cases of paralytic polio observed in that group
FalseReportsthe number of cases initially reported as polio, but later determined not to be polio in that group
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.
K. A. Brownlee (1955). "Statistics of the 1954 Polio Vaccine Trials", Journal of the American Statistical Association, 50, 1005-1013.
data(PolioTrials)
## maybe str(PolioTrials) ; plot(PolioTrials) ...
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