thank you! but Wooldridge's slope coefficients are -0.126 and 0.076 respectively.

On Sun, Dec 1, 2013 at 5:24 PM, Allin Cottrell <cottrell@wfu.edu> wrote:

On Sun, 1 Dec 2013, Allin Cottrell wrote:Ah, maybe you don't have to do that. You will get wrong results from the

> On Sun, 1 Dec 2013, Qi Shi wrote:

>

>> 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.

>

> Please post the results shown by Wooldridge, in as much detail as possible. I

> don't have his book to hand at present.

above becaause you did not define the dataset as a panel before doing

first-differencing. You need

open airfare.dta

setobs id year --panel-vars

...

Then you get:

Model 1: Pooled OLS, using 2298 observations

Included 1149 cross-sectional units

Time-series length = 2

Dependent variable: d_lfare

const 0.0391942 0.00252693 15.51 1.12e-51 ***

coefficient std. error t-ratio p-value

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

d_lfare_1 -0.134426 0.0189432 -7.096 1.70e-12 ***

d_concen 0.105206 0.0344988 3.050 0.0023 ***

Mean dependent var 0.035789 S.D. dependent var 0.120723

Sum squared resid 32.57246 S.E. of regression 0.119134

R-squared 0.027014 Adjusted R-squared 0.026166

F(2, 2295) 31.85930 P-value(F) 2.25e-14

Log-likelihood 1629.799 Akaike criterion -3253.599

Schwarz criterion -3236.379 Hannan-Quinn -3247.320

Does this agree with Wooldridge?

Allin Cottrell

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