Bookmark and Share

Notice: On March 31, it was announced that Statalist is moving from an email list to a forum. The old list will shut down at the end of May, and its replacement, statalist.org is already up and running.


[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

st: Interpreting coefficients of (logX)^2 variable in pooled OLS regression [SEC=UNOFFICIAL]


From   "DU,Lucy" <Lucy.Du@deewr.gov.au>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   st: Interpreting coefficients of (logX)^2 variable in pooled OLS regression [SEC=UNOFFICIAL]
Date   Sat, 25 May 2013 11:08:09 +1000

Unofficial
Hi All

I've been working on this research question using panel data set and am having difficulties interpreting my stata output.

Dataset: airfare.dta available on http://www.stata.com/texts/eacsap/.

Research question: How certain key variables affect airfares in the U.S. market. In the near future

I ran a pooled OLS regression: regress lfare ldist ldistsq y98 y99 y00

Where:
lfare - log transformed airfare variable ldist - log transformed distance variable ldistsq - (ldist)^2 y98, y99, y00 - year dummy variables

I understand how to interpret coefficients under a log-log transformed model, and coefficients where it's a quadratic model, but when it's a quadratic log transformed variable I'm completely stuck!

My output is as follows:

. regress lfare ldist ldistsq y98 y99 y00

      Source |       SS       df       MS              Number of obs =    4596
-------------+------------------------------           F(  5,  4590) =  581.09
       Model |  339.211826     5  67.8423653           Prob > F      =  0.0000
    Residual |  535.882547  4590   .11675001           R-squared     =  0.3876
-------------+------------------------------           Adj R-squared =  0.3870
       Total |  875.094374  4595  .190444913           Root MSE      =  .34169

------------------------------------------------------------------------------
       lfare |      Coef.   Std. Err.      t    P>|t|     [95% Conf. Interval]
-------------+----------------------------------------------------------
-------------+------
       ldist |   -.783627   .1298635    -6.03   0.000    -1.038222   -.5290322
     ldistsq |   .0897726   .0098112     9.15   0.000     .0705379    .1090072
         y98 |    .024341   .0142555     1.71   0.088    -.0036067    .0522887
         y99 |   .0350861   .0142555     2.46   0.014     .0071384    .0630338
         y00 |   .0959191   .0142555     6.73   0.000     .0679714    .1238668
       _cons |   6.239633   .4270934    14.61   0.000     5.402325    7.076942
------------------------------------------------------------------------------

Can someone explain how I interpret the coefficients for ldist and ldistsq?

Many thanks!!

Notice:

The information contained in this email message and any attached files may be confidential information, and may also be the subject of legal professional privilege. If you are not the intended recipient any use, disclosure or copying of this email is unauthorised. If you received this email in error, please notify the sender by contacting the DEEWR Switchboard on 13 33 97 (1DEEWR) during business hours (8am - 5pm Local time) and delete all copies of this transmission together with any attachments.


*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/faqs/resources/statalist-faq/
*   http://www.ats.ucla.edu/stat/stata/


© Copyright 1996–2014 StataCorp LP   |   Terms of use   |   Privacy   |   Contact us   |   Site index