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st: Logarithmic transformation in psm results


From   s <[email protected]>
To   [email protected]
Subject   st: Logarithmic transformation in psm results
Date   Thu, 17 Mar 2011 11:54:56 +0100

Dear statalisters,

I'm estimating propensity score matching (with psmatch2 routine) for a sample of firms participating in a program. My outcome variable (turnover of the firm) is expressed in logarithm, and the results are similar to these:

----------------------------------------------------------------------------------------------------------------------
Sample Treated Controls Difference S.E. T-stat
----------------------------+----------------------------------------------------------------------------------------

Unmatched | 13.2005389 8.90516337 4.29537557 .323484337 13.28 ATT | 12.9789829 12.284779 .694203895 .303516206 2.29
----------------------------+----------------------------------------------------------------------------------------

How can I transform the results in order to interpret this results in terms of the original values. My doubt arise mainly because when I estimate the ATT using the original variable expressed in monetary units the value corresponding to treated and controls not coincide with the transformed values
of the results in logarithms.

------------------------------------------------------------------------------------------------------------------------------
Sample Treated Controls Difference S.E. T-stat
----------------------------+-----------------------------------------------------------------------------------------------
Unmatched | 3940905.5 642598.305 3298307.2 266059.508 12.40 ATT | 2687231.69 2091249.89 595981.797 631105.497 0.94
----------------------------+-----------------------------------------------------------------------------------------------

Thanks in advance for your help,

Sergio

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