Tagged Questions

4
votes
2answers
409 views

Relative variable importance with AIC

I am confused and just need some confirmation about calculating the relative variable importance value for the co-variates I used in AIC model selection procedures. I know that there is this one ...
3
votes
0answers
48 views

Nesting, sort-of: Multiple observations mapping to a single DV measure?

This is a made up example, but it gets to a point I am trying to figure out. I know that you can use a nested model if your IVs are collected in clusters -- for example, if you want to model the ...
2
votes
2answers
177 views

How to conduct predictor selection in a generalized linear mixed model?

I have 18 predictors in a binary generalized linear mixed model (repeated measurements, over a 1000 subjects). I would like to trim the model a bit and remove some noise and useless predictors. ...
0
votes
2answers
133 views

Selecting the best indicator of disease progression

Quite a while ago, I asked a question for which Peter Ellis provided a very interesting answer. Now I'd like to follow on that and have your comments and ideas on how to actually put it to use. I try ...
3
votes
2answers
214 views

Is it OK to fit random effects before fixed effects?

I'm using lmer to analyse my data, building nested models and using anova() to compare them against each other in an incremental way. Now, I know enough to only test a single term at a time (i.e. only ...
3
votes
2answers
378 views

Following up a three-way interaction found with (mixed) model comparison

I hope this isn't a silly question, I'd like some advice on following up a threeway interaction in a mixed effects model. I've been building my models incrementally, like this: ...
2
votes
1answer
235 views

Relative variable importance values vs. magnitude of effect

I have ran a series of models to see which best fit the response variable and I got the following (for the model average of all models with a $\Delta AIC < 2$). I am currently learning models so ...
1
vote
2answers
315 views

Interaction term as a dependant variable in LMM with R

In a longitudinal study, two groups of subjects have been measured over a period of two years at 6 months intervals. During these measurements subjects have been assessed with a series of $k$ measures ...
2
votes
1answer
565 views

Linear mixed model, negative information criteria values and Hessian matrix not positive definite

I am analyzing (in SPSS 19) the data from a field experiment using a Linear Mixed Model with Repeated Measures. When checking the model, I always obtain negative values in the information criteria ...
0
votes
3answers
202 views

How to select best model out of linear, quadratic, and a model involving an exponential? Are the models nested?

I'm examining the growth rate of species en function of ion carbonate. For each specie, I have different measured of ion carbonate, it can be in different temperature or pH. For each measure, I'm ...
12
votes
4answers
897 views

Comparing mixed effect models with the same number of degrees of freedom

I have an experiment that I'll try to abstract here. Imagine I toss three white stones in front of you and ask you to make a judgment about their position. I record a variety of properties of the ...
13
votes
4answers
13k views

Negative values for AICc (corrected Akaike Information Criterion)

I have calculated AIC and AICc to compare two general linear mixed models; The AICs are positive with model 1 having a lower AIC than model 2. However, the values for AICc are both negative (model 1 ...