which of the following is a measure of the shared variance of the stock return _______. why is the pca often time-varying when is the explained variance compared to principal components what is common component of pca how to compare the principal components of the stock returns how to calculate the common component of a stock return what is principal component of stock return is common component a variable when compared the principal components of stock returns by the second principal component how would we compare variance over time how to compare principal components which measure is not consistent when the number of pca variables changes over time? why do we compare the principal components over time how to compare pca why do stocks vary over time with time when should stock returns be calculated as principal component when do you compare principal components which of the following would be a measure of the co-movement of stock returns? what is the purpose of the common component of stock returns how to compare principal components of stock returns