This note discusses some aspects of the paper by Hu and Tsay (2014), "Principal Volatility Component Analysis". The key issues are considered, and are also related to existing conditional covariance and correlation models. Some caveats are given about multivariate models of time-varying...

This paper explores a variety of potential issues one has to address when estimating intergenerational mobility with historical data. Many studies are potentially affected by bias originating from individuals emigrating and thus dropping out of the sample, missing information on the life-cycle,...