Hi,

I tried to post the below message and it was rejected because I hadn't yet
received my subscription to the group.

Can it be posted now?

Cheers,
Thanks very much for all your dedication to this project!
Dalal


MESSAGE I ATTEMPTED TO POST BELOW

I am trying to code the following idea using lmer (package lme4) and
running into problems. I am also unsure that I am coding this properly and
wanted to double check, as there are not enough people in my entourage that
can do this for me.

For individual fish i of species j in lake k,
Hgijk ~ b0j[i] + b1k[i] + b2j[i]*lengthi + ei
ei ~ N(0,s2e)
b0j ~ N(mb0,s2b0)
b1k ~ go + g1*chlorophyll-ak + eb1
eb1 ~ N(0,s2b1)
b2j ~ N(mb2,s2b2)

This model says that the Hg for fish i of species j from lake k is a
function of the species, the lake, and the length of the fish. The species
effects are like intercepts – the average Hg for a particular species at
average length (if the length data are centered) in an average lake – and
they come from a normal distribution. The lake effect is itself a linear
function of chlorophyll concentration, so that lakes with higher
chlorophyll can potentially have higher or lower average Hg concentrations.
The length effects vary by species, on the assumption that Hg concentration
may change with size differently in different species (which is the case in
the systems I am working in). These length effects come from a normal
distribution.

*Problems:*
1. My original idea was to code this as such:

M.A4<-lmer(LogTHg~ Chlorophyll + Length+ (1 + Length|SpeciesCode)
+(1|Location), data=mercury.subset)

-Does this function really represent the ideas I explained above?  I am not
sure if Length is supposed to be included in 2 places as it is here
-When I run this model, the se.ceof() of Length always comes out to 0,
which doesn't really make sense.  Any ideas why this might be happening?

Thank you very much for taking the time to read this and providing input.
 I appreciate it.

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