How to Perform a Shapiro-Wilk Normality Test in R (2 Examples)

This article shows how to perform a Shapiro-Wilk normality test in the R programming language.

Creation of Example Data

data(iris)                          # Iris data set as example data
head(iris)
#   Sepal.Length Sepal.Width Petal.Length Petal.Width Species
# 1          5.1         3.5          1.4         0.2  setosa
# 2          4.9         3.0          1.4         0.2  setosa
# 3          4.7         3.2          1.3         0.2  setosa
# 4          4.6         3.1          1.5         0.2  setosa
# 5          5.0         3.6          1.4         0.2  setosa
# 6          5.4         3.9          1.7         0.4  setosa

Example 1: Using shapiro.test Function to Conduct Shapiro-Wilk Normality Test

shapiro.test(iris$Sepal.Length)     # Applying shapiro.test function
#    Shapiro-Wilk normality test
# 
# data:  iris$Sepal.Length
# W = 0.97609, p-value = 0.01018

The Shapiro-Wilk test shows a significant result considering a 0.05 p-value level, i.e. the variable Sepal.Length is not normally distributed.

Example 2: Drawing Density Plot of Data

plot(density(iris$Sepal.Length))    # Non-normal density

r graph figure 1 perform shapiro wilk normality test r

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