[R-sig-ME] individual Linear mixed models

[Etn]

Thank you very much, your answer is greatly appreciated

On Mon, Sep 29, 2014 at 10:26 AM, ONKELINX, Thierry <
Thierry.ONKELINX at inbo.be> wrote:

> Another option would be to fit the model lme(y ~ Treatment*Day,  random =
> ~1|block) and then use the multcomp package to test the contrasts that you
> are interested in. E.g. only pairwise difference between treatment within
> the same day. You'll need to specify those contrasts manually.
>
> This model uses all available data to estimate the block effect.
>
> ir. Thierry Onkelinx
> Instituut voor natuur- en bosonderzoek / Research Institute for Nature and
> Forest
> team Biometrie & Kwaliteitszorg / team Biometrics & Quality Assurance
> Kliniekstraat 25
> 1070 Anderlecht
> Belgium
> + 32 2 525 02 51
> + 32 54 43 61 85
> Thierry.Onkelinx at inbo.be
> www.inbo.be
>
> To call in the statistician after the experiment is done may be no more
> than asking him to perform a post-mortem examination: he may be able to say
> what the experiment died of.
> ~ Sir Ronald Aylmer Fisher
>
> The plural of anecdote is not data.
> ~ Roger Brinner
>
> The combination of some data and an aching desire for an answer does not
> ensure that a reasonable answer can be extracted from a given body of data.
> ~ John Tukey
>
> -----Oorspronkelijk bericht-----
> Van: r-sig-mixed-models-bounces at r-project.org [mailto:
> r-sig-mixed-models-bounces at r-project.org] Namens Etn
> Verzonden: zondag 28 september 2014 17:42
> Aan: r-sig-mixed-models at r-project.org
> Onderwerp: [R-sig-ME] individual Linear mixed models
>
> Hi all,
>
> I would be very grateful if you could please give any advice...
> I am running a linear mixed model on a complete randomised block experiment
>
> blocks = 11
> treatments = 5 (A,B,C,D,E)
> data recorded on days 1, 2, 11 and 18
>
> I'm interested in looking at the difference between treatments on a
> particular day e.g. difference between treatments on day 1 (I am not
> interested in the difference between treatments on day 1 versus day 11 etc.)
>
> My question is: Is it OK to run linear mixed regression models on each day
> individually? as I'm not concerned with the changes over time.....
> (Results for individual days show a difference between treatments on day 1
> and day 2, and no difference between treatments on day 11 and 18 - this
> follows with what would be expected in reality)
>
> fit <- lme(y ~ Treatment,  random = ~1|block)
>
> Following this I run a tukey HSD to find comparison between treatments
>
>
> Is this the correct approach ? any advice is greatly appreciated
>
> Aside: I did try a more complicated model:
> fit <- lme(y ~ Treatment*day,  random = ~1|block/day) however none of the
> treatments were significant and it only showed that day
> 11 and day 8 were significantly different)
>
>
>
> Many thanks
>
> Etn
>
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