I am trying to understand how to utilize principal components as covariates for PheWAS studies. Plink can be used to generate eigenvectors, eigenvalues and additionally variant weights. It seems from what I have read that the eigenvectors used as the covariates, but I am unclear then why the eigenvalues are not included in some form. Are the eigenvalues only needed to reconstruct the genetic relationship matrix? And what are the variant weights? Are they the contribution of each variant to each of the principal components?