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st: R: Logarithmic transformation in psm results
From
"Carlo Lazzaro" <[email protected]>
To
<[email protected]>
Subject
st: R: Logarithmic transformation in psm results
Date
Thu, 17 Mar 2011 12:14:01 +0100
Sergio wrote:
"... 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".
Without other details, and provided that your problem concerns
transformation from the log scale only, the first advice is to check that,
when back transforming to the original metric (I would assume that it is
arithmetic),the sample mean is actually obtained via the following formula:
arithmetic mean=exp(ln_mean+ln_variance/2)
where:
ln_mean is the mean on the log scale;
ln_variance is the variance on the log scale.
Kindest Regards,
Carlo
-----Messaggio originale-----
Da: [email protected]
[mailto:[email protected]] Per conto di s
Inviato: giovedì 17 marzo 2011 11.55
A: [email protected]
Oggetto: st: Logarithmic transformation in psm results
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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