Exercise

Visual check of normality

Before using Grubbs' test, you should first check that the observations are plausibly normal. The hist() function in R returns a histogram of the observations, which will help you to form a judgement about the normal assumption. hist() is used as follows

hist(data, xlab = "My x-axis label", breaks = 30)

data is a vector of numeric values
breaks the number of break points used to assign the data to bins
xlab an optional character string for the x-axis label

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Use the hist() function to plot a histogram of the nitrate column.