[R-sig-ME] individual Linear mixed models

[ONKELINX, Thierry]

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
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1070 Anderlecht
Belgium
+ 32 2 525 02 51
+ 32 54 43 61 85
Thierry.Onkelinx op inbo.be
www.inbo.be

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-----Oorspronkelijk bericht-----
Van: r-sig-mixed-models-bounces op r-project.org [mailto:r-sig-mixed-models-bounces op r-project.org] Namens Etn
Verzonden: zondag 28 september 2014 17:42
Aan: r-sig-mixed-models op 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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