Log-normal MCMCglmm

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

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

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]]

-- 
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]]