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signedrank.R
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signedrank.R
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# # # Two data samples are matched if they come from repeated observations
# # of the same subject. Using the Wilcoxon Signed-Rank Test,
# # we can decide whether the corresponding data population distributions are
# # identical without assuming them to follow the normal distribution.
#
# In the built-in data set named immer,
# the barley yield in years 1931 and 1932 of the same field are recorded.
# The yield data are presented in the data frame columns Y1 and Y2.
#
#
library(MASS)
library(BSDA)
head(immer)
# Without assuming the data to have normal distribution,
# test at .05 significance level if the barley yields of 1931 and 1932 in
# data set immer have identical data distributions.
?wilcox.test
# The null hypothesis is that the barley yields of the two sample
# years are identical populations. To test the hypothesis,
# we apply the wilcox.test function to compare the matched samples.
# For the paired test, we set the "paired" argument as TRUE.
wilcox.test(immer$Y1, immer$Y2, paired=TRUE)
#As the p-value turns out to be 0.005318, and is less than the .05 significance level,
#we reject the null hypothesis.