# Do these samples look the same to you?

Examining PCA plots allows you to get a sense of similarities and differences between samples on a global scale. Using the output generated during sample QC it is straightforward to generate PCA plots of the processed data. Below is a plot for all four samples that passed QC.

Examine the plot and then consider the following statements. Which ones are true?

1. The samples cluster by condition.
2. A plot like this can be created with the plotPrincomp() function.
3. Using a PCA plot it is easy to see which peaks differ the most between groups.