Comments on: Panel Data Analysis—Advantages and Challenges

This paper provides an impressive, yet compact and easily accessible review of the econometric literature on panel data analysis. Professor Cheng Hsiao has succeeded in surveying, in a coherent manner, classic results as well as more challenging recent developments on nonlinear models, crosssectional dependence, and long time-series panels. The coverage of topics in the article reflects the breadth of Professor Hsiao’s important contributions to panel data econometrics over many years. In my comments I will focus on two aspects of recent work on nonlinear models. Firstly, I will discuss state dependence and dynamics from a treatment effect perspective. Secondly, I will consider the issue of choice of population framework and its implications for identifiability. Both comments are closely interconnected.