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# All Questions

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50 views

### Overfitting model or issue of categorical predictors?

Is it possible to overfit a model by virtue of having too many categorical variables? I have 3 categorical variables and my dependent measure is continuous (or a ratio I guess, I'm measuring ...
45 views

### Glmer Model selection [duplicate]

Bit stuck on how to choose between models. My goal is to evidence the direction of the regression slope (negative shows improvement in a metric, positive shows decline). Models ...
151 views

### Model selection: Two-Part Mixed Effects Model for Semi-Continuous Data

I have now been studying mixed models for about a month, I am still a pure beginner. I have zero inflated semi continuous dependent variable (yield of trees between two periods). Exploring ...
45 views

### Model selection with AIC/BIC, which variables to remove?

I am running a Generalized Linear Mixed Model analysis in SPSS 25, and have gotten to the point where I would like to justify the selection of my final model based on information criteria. However, ...
51 views

### Why does AIC model rank order change in lme models with standardization of predictor variables?

I can't figure this out. The AIC/AICc rank of my mixed effect models are different whether or not I standardize my predictor values using rescale. Note, I'm not concerned that AICc is changing, as ...
46 views

### Can I compare AIC values for similar models fitted for two samples from the same population?

If I have two samples (n=300) from the same population and I'm fitting a GLMM (Generalised Linear Mixed-effects Model) with a similar response and explanatory variables but with a completely different ...
49 views

### Comparing non-nested GLMMs with AIC

Suppose I want to compare four non-nested models: m0 = lm(y ~ 1) m1 = lm(y ~ x) m2 = lmer(y ~ 1 +(1|A)) m3 = lmer(y ~ x + (1|A)) Can we use AIC to compare ...
44 views

### Extremely large difference in AICs between two models

I am currently fitting a mixed model where I analye longitudinal trends in migration between country pairs (68335 observations nested in 6442 groups). One of the first questions I wanted to have ...
48 views

### Can you remove a factor from your model if it has a significant effect, but the removal improves AIC and R square?

I have a complex problem but the title sums it up pretty easily. I have four types of cages that manipulate water flow, but I also have an actual measure of water flow from inside the cages. I'm ...
523 views

### AIC model selection when successive models have ΔAIC <2 compared to next best model

I have a set of linear mixed effects models with which I'm changing fixed effects, and comparing AIC for model selection. Something akin to this hypothetical model set. Sample is ~750 observations so ...
666 views

### What are the consequences of including unnecessary random effects?

In mixed models (GLMMs), random effects are often used to account for non-independence between observations e.g. of the same patient, or of animals from the same farm. I sometimes see multiple random ...
132 views

### model comparison of non-nested mixed-effects regressions fit to datasets of unequal sample size

My aim is to compare the performance of non-nested but closely related mixed-effects regression models fit to two datasets of different sample size. The data was obtained from behavioral experiments ...
369 views

### How can mixed-effect and fixed-effect generalised linear models be compared using BIC?

Assuming I have two generalised linear models, one with only fixed effects and another with fixed and random effects, how can I compare which model is most parsimonious using AIC/BIC? I can only fit ...
55 views

### How can I compare two mixed models with the same variables but not the same relations between them

I have created two different models that include the same variables but not the same relations between them. ...
33 views

### Calculating DeltaAIC

I've been advised by a colleague that when performing backwards elimination for model selection using AIC as my criterion, I should remove terms individually - starting from the most complex ...
482 views

### How can I compare robust linear mixed models and get the p-values, F statistic, AIC and BIC?

I need to fit a linear mixed model but my dependent variable is has some outliers that I can't discard. Then I used the rlmer() function (...
303 views

### How to compare AIC for mixed effects vs fixed effects

I have time series data for 80 individuals and I'm trying to fit a nonlinear ODE. I am comparing the result of doing the fit separately for each individual vs. doing a mixed effects model. My approach ...
644 views

### Mixed effects model output - no difference in AIC values

In our study we are looking at the change in the numbers of acoustically tagged fish detections with respect to tidal state (ebbing, flowing), light period (dawn, day, dusk, night) and month (February,...
46 views

### AIC discordance in mixed effects modeling: which to prioritize?

I'd like to ask about mixed effects models. I'm modeling based on the significance of the likelihood ratio, within R. As a primary criterion I use the p-significance of the model comparison (...
235 views

### Comparing Multiple Model Types (Poisson, Negative Binomial, ZINB)

I'm working with OTU count data (essentially counts of clustered sequence reads), and trying to determine differential abundance of counts between two groups. As of now, we're using a method defined ...
2k views

### Linear mixed effects model and - multiplicity issue and adjusting for p-values

In our randomized controlled trial, we used linear mixed effects models to test differences between groups in changes from baseline to six months while adjusting for important covariates. We ran ...
63 views

### Inexplicable AIC/BIC growth from base model in SPSS 23 in a mixed model

I am running a mixed model with a binary dependent variable and a logit link using SPSS 23´s Generalized linear mixed model procedure. The data is multilevel (1 Subject, 5 questions/data points per ...
535 views

### Model selection for random effects: can unselected random effects be used as fixed effects?

I am working on a mixed effects model. What I would consider random effects are year, sampling transect, and sampling location. There are multiple collections taken along each transect, and multiple ...
91 views

### Model selection for nested count data

What is the best tool-box for model selection when working with nested count data? Is AICc appropriate for comparing Poisson and negative binomial mixed models? Is there anything special to the ...
2k views

### Number of parameters in mixed model

How can I tell how many parameters will be estimated for random effects in mixed models? Here is the example from the lme function in nlme: ...
2k views

### AIC and anova p in multilevel model, how to interpret?

I have a model with a random-nested factor, I am comparing it with a model without the random factor (to test significance of random factor) as follows: ...
51 views

### Duplicate AICc values for multiple models with interactions

I am going through a model selection process with a mixed-model with 3 variables: A, B, and C. B and C are orthogonal factors. B or C may interact with A, so my full model would be: fixed: ...
942 views

### Acceptable values for variance, aic and bic in multilevel models

I'm building a multilevel model from a sample of 820 observations at level 1 and 11 groups (level 2). I'm using stata xtmixed. Running the empty model (including ...
14k views

### Comparing non nested models with AIC

Say we have to GLMMs mod1 <- glmer(y ~ x + A + (1|g), data = dat) mod2 <- glmer(y ~ x + B + (1|g), data = dat) These models are not nested in the usual ...
79 views

### Choosing between two parameters in a model

I have a few parameters that are related (let's call them X1 and X2), and I want to use whichever one will provide the strongest model. The model has many other parameters. Would I simply be able to ...
792 views

### AICc and K for categorical factors and interactions

I am new to multimodel inference. I am trying to create a model that has multiple categorical factors and possible interactions. For example say that my model is... Y ~ X1 + factor(X2) + factor(X3) ...
3k views

### What is the upside of treating a factor as random in a mixed model?

I have a problem embracing the benefits of labeling a model factor as random for a few reasons. To me it appears like in almost all cases the optimal solution is to treat all of the factors as fixed. ...
6k views

### The 'best' model selected with AICc have lower $R^2$ -square than the full/global model

I have used the R lme function (nlme package) to construct linear mixed models, with a single random effect (as a random intercept) and a varIdent variance structure on a fixed effect (that is a ...
2k views

### AICc results in R

I used the model: ...
624 views

### How to obtain predicted values from a gamm() using averaged coefficients (MuMIn)?

I want to extract the predicted values from a gamm() whose coefficients have been averaged using the package MuMIn, but I'm getting an error. ...
72k views

### Negative values for AIC in General Mixed Model [duplicate]

I'm trying to select the best model by the AIC in the General Mixed Model test. The best model is the model with the lowest AIC, but all my AIC's are negative! So is the biggest negative AIC the ...
10k views

### Generalized linear mixed models: model selection

This question/topic came up in a discussion with a colleague and I was looking for some opinions on this: I am modeling some data using a random effects logistic regression, more precisely a random ...
1k views

### Using AIC to select between models that use nested and non-nested variables

I'm using SPSS to try and find a mixed model that adequate explains the data that I have. Two of the explanatory variables are closely related ('Sample group' and 'individual'), as an individual is ...
196 views

### Mixed linear models with exactly the same AIC?

I have a dataset in which I measure the response variable of a number of individual animals. I used this response variable as the dependent variable in a linear mixed model, for which I have 5 ...
10k views

### AIC, anova error: Models are not all fitted to the same number of observations, models were not all fitted to the same size of dataset

I have models like this: ...
682 views

### Selection of lme models using AIC & appropriate random effects & variance structure

I am using three categorical predictor variables $X_1$, $X_2$, $X_3$ and one continuous dependent variable $Y$, and I want to treat $X_3$ as a random effect. The simplest model I could come with: <...
688 views

### How do I setup a model with hierarchical structure using lmer in R?

I am trying to isolate the important predictors for my response variable "Y". I know that "TL" (which is an individual level predictor) affects "Y", and now I want to determine if adding the site ...
872 views

### Negative and positive AICc/BIC for two models with transformed data - how to compare?

I am using AICc for model selection for transformed data (continous variable). One model I used $\log_{10}(PWV)$ as response and the other $\log(PWV)$ as response, but I am not sure which one to use ...
10k 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 ...
290 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 ...
281 views

### Fitting an HLM model in lme4

I'm a fairly inexperienced statistician fighting a huge deadline and just need some peace of mind that I'm not making a massive error here. I'd be most grateful for pointers. I've been playing ...
2k views

### Model-selection for linear mixed models over alternative sets of parameters (nlme function in R)

My models look like: ...
3k 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 ...