Is there any good explanation about the confidence ellipse used in PCA analysis which briefly describes how to interpret the result? For example, I am looking for the following cases:
Some points are not included in the ellipse. What does that mean? How about few and large number of observations (individuals) are not included in the ellipse?
What does the angle of the ellipse reveal? For example, what is the difference between a horizontal ellipse (stretched over PC1) versus angular ellipse versus a vertical ellipse (stretched over PC2).