hi,

when I replicate Example 11.3 of Wooldridge's advance book(the second edition), i encounter a problem. To run the pooled OLS, I write

open airfare.dta

genr lfare_1=lfare(-1)

diff lare lfare_1 concen

ols d_lfare d_lfare_1 d_concen

then, I get the outputs, which is different from the results of the Book. Why? Thanks!

Model 1: OLS, using observations 3-4596 (n = 4594)

Dependent variable: d_lfare

Heteroskedasticity-robust standard errors, variant HC1

coefficient std. error t-ratio p-value

------------------------------------------------------------

const 7.61258e-05 0.00427816 0.01779 0.9858

d_lfare_1 −0.114781 0.0104885 −10.94 1.56e-27 ***

d_concen −0.292149 0.0520106 −5.617 2.06e-08 ***

Mean dependent var 0.000068 S.D. dependent var 0.294573

Sum squared resid 386.0532 S.E. of regression 0.289981

R-squared 0.031358 Adjusted R-squared 0.030936

F(2, 4591) 70.98109 P-value(F) 4.37e-31

Log-likelihood −830.0114 Akaike criterion 1666.023

Schwarz criterion 1685.320 Hannan-Quinn 1672.815