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Estimating p-value for fixed effect which occurs also in interaction
3 messages · Martin Heggli, David Duffy, Geoff Brookshire
On Tue, 8 May 2012, Martin Heggli wrote:
Dear listers, I am evaluating an experiment in plant ecology. Since the experiment has both crossed and nested random factors and the data are unbalanced, I decided to use linear mixed effects models (lmer from lme4). Right now, I am struggling to determine the significance of the fixed factors. I tried to estimate the p-value for the fixed factors by dropping individual factors from the model and comparing the two models with anova (cf. code below). However, I run into trouble when I try to drop the factor Origin from the model which occurs also in the Origin:Soil interaction term.
The main effect of Origin gets absorbed by Origin:Soil ie you have only changed the interpretation. If Origin:Soil is necessary to the model, you probably want to examine Soil within each level of Origin. Just 2c, David Duffy.
Here's a similar question from a few months ago, with Ben Bolker's very helpful response: https://stat.ethz.ch/pipermail/r-sig-mixed-models/2011q3/006690.html cheers, geoff
On Tue, May 8, 2012 at 7:37 PM, David Duffy <David.Duffy at qimr.edu.au> wrote:
On Tue, 8 May 2012, Martin Heggli wrote:
Dear listers, I am evaluating an experiment in plant ecology. Since the experiment has both crossed and nested random factors and the data are unbalanced, I decided to use linear mixed effects models (lmer from lme4). Right now, I am struggling to determine the significance of the fixed factors. I tried to estimate the p-value for the fixed factors by dropping individual factors from the model and comparing the two models with anova (cf. code below). However, I run into trouble when I try to drop the factor Origin from the model which occurs also in the Origin:Soil interaction term.
The main effect of Origin gets absorbed by Origin:Soil ie you have only changed the interpretation. ?If Origin:Soil is necessary to the model, you probably want to examine Soil within each level of Origin. Just 2c, David Duffy.
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