Explained variance of a principal component (${\lambda }_j/\mathrm{tr}\Sigma$)

A population principal component explains the displayed fraction of total variance. The first $q$ components explain ${\sum }_{j\le q}{\lambda }_j/{\sum }_j{\lambda }_j$. Comparing covariance and correlation analyses requires different denominators: the original variance sum for the former and the number of nonconstant standardized variables for the latter.