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. [[alternative HTML version deleted]]