[R-sig-ME] Log-normal MCMCglmm

[Paul Johnson]

PS I should have written:

> Y = Yhat * epsilon, where epsilon ~ exp(N(0, sigma^2))


not

> Y = Yhat * exp(epsilon), where epsilon ~ exp(N(0, sigma^2))

Paul


On 28 Jul 2015, at 11:33, Paul Johnson <Paul.Johnson at glasgow.ac.uk> wrote:

> 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 Jörg,
>> 
>> 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 Jörg Albrecht <albrechj at staff.uni-marburg.de>:
>> 
>>> Hi Dani,
>>> 
>>> you could try specifying
>>> 
>>> family = "poisson".
>>> 
>>> Best,
>>> 
>>> Jörg
>>> 
>>> —
>>> Jörg 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
>>> 
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>>> 
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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
>> 
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>> 
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> 
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