Mixed (aka multilevel or hierarchical) models are linear models that include both fixed effects and random effects. They are used to model longitudinal or nested data.

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Can a random effects variable be highly and coincidentally correlated to a response variable?

Issue- I'm creating a logistic mixed model where the response variable (if a plot falls within an active bird lek area) is highly related to a term I may include as a random effects term (grazing ...
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Chosing an covariance matrix or 'repeated covariance type' spss

I'm struggeling with my choice for a covariance matrix or 'repeated covariance type' for my lineair mixed effects analysis in SPSS. I have a continuous measurement for experienced emotion(0-100), ...
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Effect in linear model versus effect in mixed model

Consider a dataset with 3 observations pertaining to 5 patients. This can be modeled in several ways, two of which are that $$ X_{ij} = \xi_i + Y_j + \epsilon_{ij}, $$ $i = \{1,..,3\}$, $j = ...
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Multiple testing & model selection using AICc

I have a situation very similar to this post. I am finding the best-fit mixed effects model among a set of 5 candidate models for 7 different dependent variables (y1 to y7) using the same dataset of ...
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1answer
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What's the interpretation of ranef, fixef, and coef in mixed effects model using lmer?

I have two observations from a person each, where every observation corresponds to a different treatment. The treatments are fixed effects, the persons are random effects. I use the command: ...
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Model selection: testing the need for random-effects terms in longitudinal data

I have longitudinal data set where each participant was observed for 12 weeks. I followed this paper: Bliese, Paul D., and Robert E. Ployhart. "Growth modeling using random coefficient models: Model ...
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1answer
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Linear mixed model with partially crossed effects

I'm new to Linear Mixed Models and I'm not sure if I'm specifying the right model. I'd appreciate any feedback that confirms / disproves my model. Here's some background about my data: I have a list ...
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1answer
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Mixed effect - Pooled ols Different results interpretation

I have a question. I have collected data regarding the performance of companies and their board structure. I want to find the effect of the Board structure upon the performance and I am using pooled ...
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Identical mixed models in SPSS and R nlme, with different degrees of freedom. Which to trust and why?

I am analyzing a multilevel dataset with an AR(1) error structure and random intercept and slope. I fit what I believe is the exact same model in SPSS and R- my coefficients and standard errors are ...
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2answers
38 views

How can I test for differences in variation between groups in a mixed model (lme4)?

I would like to test for differences in variation, not in means, between two sites. By looking at a boxplot of my data I see that bird song in one site look much more variable in length than in ...
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Setting Linear mixed model for within-subject crossed factors

I have problems in undertanding how to correctly run a mixed linear model. I have done an experiment to compare three groups (1 between-subject factor); for each subject, 2 sensory stimuli are given ...
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Formal formula for GLMM given glmer syntax

I'm looking for help writing the formal formula for a binomial mixed model with three crossed random intercepts, one numeric fixed effect, a logit link function, and a log-transformed offset term. ...
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zero estimate for value and std. error for mixed models in R

I ran an linear mixed effects model in r. The summary statistics for my fixed effects has estimates of zero but gives me a t-value and p-value (see variable Buffer_400 in image below). How do I ...
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1answer
32 views

Generalized linear mixed model - glmmADMB - date as random effect

I have a couple related questions about using a generalize linear mixed effects model to analyze data from an agricultural field experiment. I have found several posts that are similar to this ...
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15 views

What is a quasi F ratio and how to compute it in R?

I've been reading this classic study (free pdf) of false memories by Loftus & Palmer (1974) and do not understand their analysis in Experiment 1 (p. 586), particularly— a) the use of subjects as ...
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Which analysis is best for my data with repeated measures and 2 treatment groups?

I'm working in R. I have a data set of 21 fish, roughly half in each of 2 treatments. I measured their behaviour over 10 minutes and want to analyse this to look for changes over time (gradient) and ...
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1answer
30 views

Why is the coefficient in this Washington Post fixed effects regression output considered significant?

I'm trying to understand the multiple regression fixed effects model the Washington Post used for a story. See the outputs here: What is confusing me is the first predictor: ...
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gam.check() NA results (k-index, p-value) of a gam logistic regression model [closed]

I am using bam for a mixec-effects logistic regression model: b0<-bam(acc~ 1 + igc + s(ctrial, by=igc) + s(sbj, bs="re") + s(ctrial, sbj, bs="re") , data=data, family=binomial) ...
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How to perform a repeated measures test on my data in R? [closed]

I have a dataset of fish whose behaviour has been measured before and after a treatment, and there are 2 genotypes of fish which I am looking at. I'm using R but any advice on which statistical test ...
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constructing random effects design matrices for lassop{MMS}

I'd like to use elastic net regression for coefficient estimate and parameter selection on a data set that includes nested structure. I've been experimenting with lassop{MMS} to do so. I'm not a ...
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Analysis for evolution of resistance

I am looking for help on an approach for analyzing evolution of resistance. I conducted an experiment in which I exposed pathogens to a constant drug concentration over 6 weeks. At each week, I tested ...
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23 views

Why do I get chi values, when I've stated F test?

I am trying to do an lmer and find my MAM model, using the lme4 package, and have two problems/questions in that connection. Q1: My starting model is this: ...
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1answer
41 views

Why disable ridge/lasso penatly for fixed effects?

I'm running a mixed effect elastic net regression model that was built by someone else to make predictions. The features we are predicting from are included as random effects and other features are ...
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How to set lower/upper bound for LMER analysis

I'm not sure if this is possible but can I set a lower bound for my LMER analysis? i.e. so that the estimated means will not be lower than zero? Thanks
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Multilevel Power of a Mixed Model

For my dissertation I have data from 57 employees that responded the same survey on 11 occasions (i.e., 11 observations per person for each variable). All variables I am interested in (and are ...
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Linear Mixed Model with few and ranked subjects

I am studying linear mixed model recently, and my data have only 6 subjects and those are ranked groups of observations (Tier 1 customers > Tier 2 customers > Tier 3 > ... > Tier 6) The formula looks ...
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1answer
52 views

Mixed-effect model / ANCOVA with lmer in R

I have a question according the following example: What I want to find out is whether two fertilizers (A and B) have different effects on the biomass of my plants. My explanatory variable is ...
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Using a Fixed-Effects ANOVA to help decide whether to conduct a multilevel analysis

Heck et al (2013) write that Generally, the first step in a multilevel analysis is partitioning the variance (referred to as $\sigma^2$) in an outcome variable into its within- and ...
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Weighting of predictors in a temporally correlated mixed effect model

I want to investigate the impacts of historic factors (vegetation density) on biodiversity sampled in the present. These historic factors all very likely all temporally autocorrelated with each other. ...
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How is repeated-measures ANOVA a special case of linear mixed models?

In this comment @gung mentions that On a different note, I think it's fair to think of RM ANOVA as a special case of linear mixed models. and a subsequent comment concurs with this. I ...
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experimental design lme

I have a question about my experimental design and how to treat it statistically. Briefly, I am interesting in how herbicide application affects plant biomass and is it any differences between ...
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28 views

Multilevel Principal Component Analysis

I needed to run a PCA on a dataset with a multilevel structure. My question is similar to the one asked here: Principal components analysis on nested data In my case, however, the two levels are ...
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The name of technique, when main models explicitly split to submodels

For my project I work with some kind of random forest. Until recently I've had a huge dateset and I just built one model(one random forest) based on this dateset. The quality of this model was not ...
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Is there anything wrong with keeping random intercept and slope terms that are perfectly correlated with oneanother?

I am following the advice to "keep it maximal", and am analyzing the results from several psycholinguistic experiments. My main interest is in the fixed effects, with the random effect terms in there ...
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Predicting a parameter using the estimates of a series of studies, using study location and year as random effects

I would like to ask whether my analysis design is correct. I gathered all the trials on a series of drugs for a certain condition (second line therapy for advanced/metastatic lung cancer), published ...
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24 views

How to test the inclusion of a single random effect in glmer?

Suppose I have two models: m1=glm(DV~IVs) m2=glmer(DV~IVs+(1|Subject)) How can I test the inclusion of that random intercept in R? I know that I can't use ...
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1answer
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Mixed-effect models for repeated measures - problems with the “Significance level”

I am trying to fit a linear mixed-effect model to my dataset to see the relationship between a self-reported questionnaire and some physiological data. I've created a first model including all the ...
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1answer
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Interpreting results of a Linear Mixed effect Model

I am trying to implement a Linear Mixed-Effects Model in Matlab. I have many repeated measures of some features in a longitudinal data set of 51 people. I considered a random intercept that varies by ...
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ICC as expected correlation between two randomly drawn units that are in the same group

In multilevel modelling the intraclass correlation often gets calculated from a random-effects ANOVA $$ y_{ij} = \gamma_{00} + u_j + e_{ij} $$ where $u_j$ are the level-2 residuals and $e_{ij}$ are ...
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Difference between weighting and replicating observations in linear regression

I have a model in which each case is summary statistic of many observations. I am using a mixed effect model (lmer() in R) for prediction and I thought to give ...
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8 views

Fixed-effects variable selection for mixed-effects regression

Does anybody know if it is possible to apply some "feature selection" algorithm to a dataset prior to creating a mixed-effects regression model? I am trying to implement such a modelling in Matlab, ...
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Interpreting random slope for a dataset with missing data in mixed model

I am struggling to understand the meaning of random effect for the dataset with missing data based on mixed model, I am appreciated if anyone can help. Here is an example. let us say we have 20 ...
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Controlling for variables with lmer (R)

I am using lmer (from the lme4 R package) on a dataset with 6 variables: SubjectID, ImageID, Category, Brightness, Contrast and ResponseTime, where the last three are continuous variables. (and yes, ...
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In a mixed effects model, how do you determine when the slope and intercept should be independent?

This is a question regarding the theory underlying mixed effects models, specifically a general rule of thumb that can be used to determine the structure of random-effect portion. Here's what I ...
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Mixed-effects model: basic questions

I am trying to implement a mixed-effects regression model in Matlab to see the correlation between self-reported stress levels and some physiological features. Data comes from a longitudinal study so ...
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1answer
33 views

Random effects for second order in R mixed models

I am fitting a mixed effects model in R using nlme lme(y~x+I(x^2),random=~x|subject,data=train) Is this the correct way or should it be ...
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1answer
32 views

meta-analysis mixed model - polygons based on meta-regression

When using meta-regression with factor moderators, result differ a bit from using seperate estimation based on subgroup, even if the same model (mixed effects) is used for both. I understand the ...
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RJAGS bayesian approach of mixed effects model

Why my posterior result always shows that the sigma and sigma.c estimates to be around 50? It should not be that large as I know from another approach of analysis and also summary of the data. Is it ...
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robust mixed models 3 time points (y-side) and high dropout

I am running the model in R: model = rlmer(Tau ~ tract_FA_avg + (1|Subject), data=long2) (robust as I have outliers) Since I am relatively new to mixed ...
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Hierarchical, Linear mixed-effects model

The aim of my task is to ""investigate whether and how various factors affect the evolution of the life expectancy"". The data includes country, year (just a few and discontinuous like 1990 2007 2011, ...