Adding confidence intervals to a qq plot?

Question

Is there a way to add confidence intervals to a qqplot?

I have a dataset of gene expression values, which I've visualized using PCA:

pca1 = prcomp(data, scale. = TRUE)

I'm now looking for outliers by checking the distribution of the data against the normal distribution through:

qqnorm(pca1$x,pch = 20, col = c(rep("red", 73), rep("blue", 33)))

qqline(pca1$x)

This is my data:

data = [2.48 104 4.25 219 0.682 0.302 1.09 0.586 90.7 344 13.8 1.17 305 2.8 79.7 3.18 109 0.932 562 0.958 1.87 0.59 114 391 13.5 1.41 208 2.37 166 3.42]

I would now like to plot 95% confidence intervals to check which data points lie outside. Any tips on how to do this?

Answer 1

The library car provides the function qqPlot(...) which adds a pointwise confidence envelope to the normal qq-plot by default:

library(car)
qqPlot(pca1$x)