Message-ID: <353CAFC4-8F52-4AF8-AC2B-420DFF512BF9@glasgow.ac.uk>
Date: 2015-07-28T10:33:04Z
From: Paul Johnson
Subject: Log-normal MCMCglmm
In-Reply-To: <CAN3C_1C_Lgb+CsJN=PpkKQa33_9TS4H7apQqKsSa_YPb3rhToA@mail.gmail.com>
Hi Dani,
Can you explain with a formula what you mean by the difference between a model with log-normal errors and a model with normal errors where the response is log-transformed? As the errors are log-normal, i.e. strictly positive, they presumably can?t be additive. Are they multiplicative? If they are then logging the predictor will result in an additive model with normal errors.
E.g. a multiplicative model with lognormal errors:
Y = Yhat * exp(epsilon), where epsilon ~ exp(N(0, sigma^2))
Log it:
log(Y) = log(Yhat) + log(epsilon)
which is an additive model with normal errors with the response log-transformed.
Best wishes,
Paul
On 28 Jul 2015, at 09:47, Daniel Sol <dsolrueda at gmail.com> wrote:
> Hi J?rg,
>
> Thanks a lot for the suggestion. I actually have tried to use a Poisson
> error, but it looks like my data best fit a log-normal distribution.
>
> Best,
>
> Dani
>
> 2015-07-28 10:40 GMT+02:00 J?rg Albrecht <albrechj at staff.uni-marburg.de>:
>
>> Hi Dani,
>>
>> you could try specifying
>>
>> family = "poisson".
>>
>> Best,
>>
>> J?rg
>>
>> ?
>> J?rg Albrecht, PhD
>> Postdoctoral researcher
>> Institute of Nature Conservation
>> Polish Academy of Sciences
>> Mickiewicza 33
>> 31-120 Krakow, Poland
>> www.carpathianbear.pl
>> www.globeproject.pl
>> www.iop.krakow.pl
>>
>> Am 25.07.2015 um 11:31 schrieb Daniel Sol <dsolrueda at gmail.com>:
>>
>> Hi everybody,
>>
>> I have trouble finding how to implement a MCMCglmm with log-normal error. I
>> know some people just log-transform the response variable, but this is not
>> the same.
>>
>> Many thanks in advance,
>>
>> Dani
>>
>> --
>> Daniel Sol
>> CREAF (Centre for Ecological Research and Forestry Applications)
>> CSIC (Spanish National Research Council)
>> Bellaterra, Catalonia E-08193, Spain
>> TEL: +34 93-5814678
>> FAX: +34 93-5814151
>> E-MAIL: d.sol at creaf.uab.es
>> Webpage: http://dsolrueda.wix.com/sol-group
>>
>> [[alternative HTML version deleted]]
>>
>> _______________________________________________
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>>
>>
>>
>
>
> --
> Daniel Sol
> CREAF (Centre for Ecological Research and Forestry Applications)
> CSIC (Spanish National Research Council)
> Bellaterra, Catalonia E-08193, Spain
> TEL: +34 93-5814678
> FAX: +34 93-5814151
> E-MAIL: d.sol at creaf.uab.es
> Webpage: http://dsolrueda.wix.com/sol-group
>
> [[alternative HTML version deleted]]
>
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