请问这些写得是什么啊？不太懂，是面板数据的那一部分知识？

Cross-sectional/time seriesdata. Panel data. Longitudinal data.

t = time, i = firms, etc.

    yit = b0 + b1 x1it + b2 x2it + uit                       (i)

      

(i) is pooled model,constant coefficient model. b0,b1, b2, etc. the same for allobservations. uit ~ N (0, s2).

But could well bedifferences between the cross-sections e.g. firms.

FixedEffects Model

    yit = bi + b1 x1it + b2 x2it + uit                        (ii)

      

(ii) is fixed effectsmodel. The constant (b0)differs for each i. Hence bi.uit ~ N (0, s2).

RandomEffects Model

    yit = b0 + b1 x1it + b2 x2it + uit                       (iii)

uit= ui + vit

ui~ N (0, su2)

vit~ N (0, sv2)

      

(iii) is random effectsmodel. The error term (ui) differs for each i.