without much luck i also posted the following question at stackexchange:

I am trying to develop a mixed effects model on a data set with repeated
measures.

`Met` is measured on a series of randomly selected days on 24 samples
submitted to 3 treatments (`Treat`, with levels `c`, `uc` and `ga`)

The levels of `Met` change due to differences in weather conditions during
the days (`Date`). Date thus becomes a second random effect of the model
(next to the items sampled (`ID`))

My main interest is to see whether `Treat` has a significant effect on
`Met` across days.

some sample data:

    # create example data frame
    ID     <-  factor(rep(c("a", "b", "c", "d", "e", "f", "g", "h", "i",
"j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x"),
6))
    Treat  <-  factor(rep(c(rep("c",8), rep("uc",8), rep("ga",8)), 6))
    Date   <-  factor(rep(c(rep("10/06/2007",24), rep("19/06/2007",24),
rep("12/07/2007",24), rep("21/07/2007",24), rep("11/08/2007",24),
rep("12/08/2007",24)), 1))
    Met    <-  as.numeric(c(rnorm(8,5,2),   rnorm(8,7,2),   rnorm(8,9,2),
                            rnorm(8,150,2), rnorm(8,152,2), rnorm(8,154,2),
                            rnorm(8,9,2),   rnorm(8,11,2),  rnorm(8,13,2),
                            rnorm(8,8,2),   rnorm(8,10,2),  rnorm(8,12,2),
                            rnorm(8,2,2),   rnorm(8,4,2),   rnorm(8,6,2),
                            rnorm(8,3,2),   rnorm(8,5,2),   rnorm(8,7,2)))
    ww     <-  gl(1,1,144)

    lys.data  <-  data.frame(ID, Treat, Date, Met, ww)
    head(lys.data)

    # set contrasts of data frame
    lys.data$Treat   <-  factor(lys.data$Treat,     levels=c("c", "uc",
"ga"))

Then the analysis:


    library(nlme)

    anova.lme.001  <-  anova(lme(Met ~ Treat, data = lys.data,

 random=list(ww=pdBlocked(list(pdIdent(~Date-1),pdIdent(~ID-1))))))
    anova.lme.001

>From the results I get it seems that I am not doing what I assume I am
doing as the denominator degrees of freedom seem incorrect and increase
with the number of repeats (reporting several hundreds or even  thousands
of den. degrees of freedom just feels wrong).

Who can help me out here or point me into the right direction?
Am I going wrong with the way the I am representing the nesting of the
data? (I assume there is none).

many thanks in advance,

thijs van den bergh

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