[R-sig-ME] multilevel nested data in lmer models

[Douglas Bates]

On 2/15/07, Hallstrom, Wayne (Calgary)
<Wayne.Hallstrom at worleyparsons.com> wrote:
> I have what should be a simple question about structure of the formula
> for an lmer model. However, I can find no detailed description of how to
> write multilevel nested formulas for lmer though so I need some advice.
>
> Count data were collected at 10 subsample locations nested within each
> of 7 general locations over a 20 year period of repeated measures. At
> each of the 7 general locations there was a treatment applied partway
> through the 20 year period to 1/2 of the subsample locations.
>
> I thought running the lmer routine with the following general formula
> setup would account for the fixed effects of the treatment and the
> random effects of the nesting structure. A Quasipoisson distribution was
> used to account for over/underdispersed data.
>
> model1 <- lmer(count ~ a + (1 | b / c), dataset)
>
> This model returns an error message though - "too many groups, only the
> first is used".  I thought this formula should account for the grouped
> and nested data structure. I have used this model structure with a
> different dataset and a similar lmer model and it worked fine, nesting
> the one explanatory variable within the other in the proper arrangement
> and producing reasonable results. This time it does not work. Is there a
> different way the formula should be set up?

Could you show us the structure of the data set (use

str(dataset)

and a transcript of your attempt to fit the model?  The reason I ask
is because I don't think that error message occurs in the lme4
package.  I just did a quick check on both the R and the C sources and
I can't find it.

Also please include the output of

sessionInfo()

in your message so we know what versions of various packages you are using.

> Someone with more background in this method must have had a similar
> problem before while using this lmer routine, so hopefully another
> perosn on the list can describe/advise how to deal with this kind of
> nested data and what may be the problem here...
>
>
>
> Thank you,
>
> Wayne Hallstrom
>
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