# Re: st: Interpretation of regressionmodel of ln-transformed variable

 From Maarten buis To statalist@hsphsun2.harvard.edu Subject Re: st: Interpretation of regressionmodel of ln-transformed variable Date Thu, 6 Nov 2008 10:15:04 +0000 (GMT)

```As you can see (by looking at the column "Obs"), both the Geometric and
Harmonic means ignore observations with LOS=0. If you think that those
observations can truely exist and are not some data error, than that
would be a strong argument in favor of the arithmetic mean.

If you think that those observations are data errors, then you should
ignore those observations anyhow, or try to recover their true value.
In those cases the choice between the different types of means can be
based on substantive reasons, see for instance (Avital and Falk 2006).

Hope this helps,
Maarten

Lann, Avital and Ruma Falk (2006) "Tell me the method, I'll give you
the mean", The American Statistician, 60(4): 322--327.

> There are a total of 303 of 37736 patients with LOS=0. I looked for
> the different means in the two groups. Obviously the difference is
> largest for the arithmetic means and almost absent for the harmonic.
> Can you give an advice on what mean to use when reporting on LOS?
>
> ->	lapscopiintention = 0
>
> 	Variable     Type	Obs	Mean	[95% Conf.	Interval]
>
> 	vtid  Arithmetic	28808	2.985178	2.924702	3.045654
> 	Geometric	28586	2.322214	2.304817	2.339742
> 	Harmonic	28586	1.931199	1.918483	1.944085
>
>
>
> ->	lapscopiintention = 1
>
> 	Variable     Type	Obs	Mean	[95% Conf.	Interval]
>
> 	vtid  Arithmetic	8928	2.792451	2.745438	2.839463
> 	Geometric	8847	2.294519	2.26541	2.324002
> 	Harmonic	8847	1.933647	1.911211	1.956615

-----------------------------------------
Maarten L. Buis
Department of Social Research Methodology
Vrije Universiteit Amsterdam
Boelelaan 1081
1081 HV Amsterdam
The Netherlands

Buitenveldertselaan 3 (Metropolitan), room N515

+31 20 5986715

http://home.fsw.vu.nl/m.buis/
-----------------------------------------

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```