Message-ID: <563B4899.3050705@ti.bund.de>
Date: 2015-11-05T12:16:25Z
From: Quentin Schorpp
Subject: Small sample Size; repeated measurements binomial glmer
Hello,
I searched a lot in the internet, but i didn't find sufficient information.
I believe I've got a very simple study design, however there are some
characteristics taking me to the brink of possible.
I have two sampling campaigns, autumn year 1 and autumn year 2,
I sampled five agricultural fields of different ages, but each age_class
has got only 3 repetitions.
My response is proportion of fungal feeding species.
I am interested in the effect of age classes (increase over time) and if
this effect is reflected during the time of sampling.
Since i should be able to observe an increase during a 1 year time
interval, then.
My Model is:
glmer(response ~ age_class*autumn + (1|field), family="binomial",
weights=total number of Individuals, data)
However, I have the following problems:
1 - My N = 30, but my N(group) = 3
1 - I don't know the power of my analysis
2 - I'm not able to drop Outliers from the data (or am I?)
3 - my random factor has only 2 levels, so N(random) = 2
I think in Bolker et al. (2008) und Zuur et al. (2009) st. is said about
that there is no need to use random factors when N(random) = 2
Since I am quite confused about my opportunities to handle patterns in
residuals of the above model, I'm asking you about your opinions. Have i
chosen the right Model formulation?
I think I'd feel more confident with a non parametric test, sth. like a
rank based estimation of mixed effects nested models (rlme package), for
which i found not a single example how to use them with repeated
measures (also for PERMANOVA), or sth. else.
At least i need to report an Anova table and pairwise comparisons
yours sincerely,
Quentin
--
Quentin Schorpp, M.Sc.
Th?nen-Institut f?r Biodiversit?t
Bundesallee 50
38116 Braunschweig (Germany)
Tel: +49 531 596-2524
Fax: +49 531 596-2599
Mail: quentin.schorpp at ti.bund.de
Web: http://www.ti.bund.de
Das Johann Heinrich von Th?nen-Institut, Bundesforschungsinstitut f?r L?ndliche R?ume, Wald und Fischerei ? kurz: Th?nen-Institut ?
besteht aus 15 Fachinstituten, die in den Bereichen ?konomie, ?kologie und Technologie forschen und die Politik beraten.
Quentin Schorpp, M.Sc.
Th?nen Institute of Biodiversity
Bundesallee 50
38116 Braunschweig (Germany)
Tel: +49 531 596-2524
Fax: +49 531 596-2599
Mail: quentin.schorpp at ti.bund.de
Web: http://www.ti.bund.de
The Johann Heinrich von Th?nen Institute, Federal Research Institute for Rural Areas, Forestry and Fisheries ? Th?nen Institute in brief ?
consists of 15 specialized institutes that carry out research and provide policy advice in the fields of economy, ecology and technology.
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