Panel data is sorted by itself. The paper needs panel data and section data to sort out. Panel data refers to both cross-sectional data and time series data, and its cross-sectional data has no advantage. When using stata to estimate the panel data, select xtreg command for fitting. Before the model estimation of panel data, it is necessary to determine the dimension of panel data. Panel data has both cross-sectional data and time series, but stata can't automatically identify them, so stata must know which part is cross-sectional data and which part is time series.