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An independent agency measures the sodium content in 20 samples from source x and in 10 samples from source y and stores them in the data frame WATER.
x
y
WATER
A data frame with 30 observations on the following 4 variables:
x (sodium content measured in mg/L)
y (sodium content measured in mg/L)
sodium (combined sodium content measured in mg/L)
sodium
source (a factor with levels x and y)
source
Ugarte, M. D., Militino, A. F., and Arnholt, A. T. 2015. Probability and Statistics with R, Second Edition. Chapman & Hall / CRC.
# NOT RUN { ggplot(data = WATER, aes(x = sodium, y = ..density.., fill = source)) + geom_density(alpha = 0.2) t.test(sodium ~ source, data = WATER, alternative = "less") # }
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