[R-sig-ME] lme AR1 structure, plus cross-posting etiquette (was Re: lme:correlations tructure AR1 and random factor)

Ben Bolker bbolker at gmail.com
Wed Mar 30 20:08:54 CEST 2011

On 11-03-30 11:52 AM, Christoph Scherber wrote:
> Dear Yvonne,
> You need to take care that you have exactly the same nesting terms in
> the "correlation" and "random" component.
> You *could* possibly try:;
> random=~session|field correlation =corCAR1(form = ~ session)
> All the best Christoph
> Yvonne Fabian wrote:
>> Dear mixed models specialists,
>> I tried these model to run in the package nlme, but allways got the
>> same error message...
>> I have a timeseries correlation in 5 sessions within 12 fields with
>> 12 traps per field.
>> res2a <- lme(response~x+y+z+treatment,correlation = corCAR1(form =
>>  ~ session|trapfield), random=~1|field, na.action=na.omit, 
>> data=plates, method="ML")
>> Error: Incompatible formulas for groups in "random" and 
>> "correlation" I do not want to use trapfield as a random factor and
>> using only session|field in the correlation term leaves me with a
>> errormessage that there have to be unique values. Do you have any
>> suggestions what to do?
>> thanks a lot! Yvonne

  Didn't I answer this yesterday?


  Grumpy meta-comment: this has happened a few times.  Someone
posts to an R list (or StackOverflow), I (or others) answer it, and then
they ask the question a day or two later on a different list.  I can
appreciate (temporally separated) cross-posting if no-one answers on the
first list, but why ask again if the question has already been answered?

 Is it:

(1) the original poster [OP] isn't subscribed to the list, and the
answer has only been posted to the list and not e-mailed back to the OP
[it's considered good etiquette to subscribe to the list at least long
enough to see answers that are posted and not e-mailed rather than
saying "I'm not subscribed, please e-mail me directly" -- if others can
bother to take the time to answer the question, you should be able to
take the time to subscribe to the list at least temporarily]

(2) the OP didn't understand the answer. In that case the right thing to
do is to respond to the post on the original list, explaining as best
you can what you didn't understand, so that (a) other list respondents
can help out if the original answerer is too busy (b) other list
followers (present and future) can see the whole conversation, and maybe
get a better understanding of the answers themselves.

(3) the OP understood the answer, but didn't like it and so hoped for a
different answer.  It is possible that exposing the question to a new
set of people will get a different/better answer, but it is at least
polite and saves time to post a new message saying "I asked this
question a few days ago on list xxx and got answer yyy from person zzz.
 That answer doesn't work for me [for the following reasons ...], and I
was hoping that someone on this new list would be able to point me to a
different solution to my question" (rather than just asking the same
question again in the same form, as though it is a brand-new question).
 That way, (a) the original answerer is credited, and (b) everyone's
time won't be wasted giving the same answer as before.

  I don't mean to give offense, but as someone who has been on the R
lists for a long time and takes a lot of effort to answer questions, I
feel entitled to pontificate a little bit about list etiquette. (Or else
it's just the lunchtime caffeine speaking ...)

  Ben Bolker

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