Previously, we described the essentials of R programming and provided quick start guides for importing data into R.
Pleleminary tasks
Launch RStudio as described here: Running RStudio and setting up your working directory
Prepare your data as described here: Best practices for preparing your data and save it in an external .txt tab or .csv files
Import your data into R as described here: Fast reading of data from txt|csv files into R: readr package.
Example data
Here, we’ll use the built-in R data set named ToothGrowth.
# Store the data in the variable my_data
my_data <- ToothGrowthCreate QQ plots
The R base functions qqnorm() and qqplot() can be used to produce quantile-quantile plots:
- qqnorm(): produces a normal QQ plot of the variable
- qqline(): adds a reference line
qqnorm(my_data$len, pch = 1, frame = FALSE)
qqline(my_data$len, col = "steelblue", lwd = 2)
It’s also possible to use the function qqPlot() [in car package]:
library("car")
qqPlot(my_data$len)
As all the points fall approximately along this reference line, we can assume normality.
See also
Infos
This analysis has been performed using R statistical software (ver. 3.2.4).