# Questions tagged [mixed-model]

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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### Linear Mixed Effects Model in R [closed]

I am trying to understand the outputs from the lme() function in R. I have the following model: $$X_i(t_{ij}) = \eta + Z_i(t_{ij})w_i + \epsilon_{ij},$$ where $\eta$ is ...
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### Am I using the right linear mixed model design for my data?

I want to move from using repeat measure ANOVAs to linear mixed models (LMM). However, where I have good intuitions about ANOVAs, LMMs are new to me. I'm using python's StatsModels as my package. Here'...
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### Effect size for mixed ANOVA

I have a mixed anova with repeated measures design: two between-subjects factors, doctor (3 levels) and method (3 levels), and one within-subject factor, time (1w, 3w, 2m, and 6m). 3 doctors would be ...
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### logistic regression with two continuous predictors

Let's say I conducted an experiment in which I measured if customers bought a particular product and also measured customer satisfaction with the shop and familiarity with that product. The dependent ...
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### zeroed random effects after fitting a mixed effect model [closed]

I am fitting a linear mixed effect model with two categorical factors: mPair with 6 levels, and spd_des with 3 levels. This is a ...
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### Is it correct to treat a confounding variable as random with mixed modelling?

In a semi-controlled experiment, seeds were sown in about 20 boxes, associated with 3 types of soil. A few months later, the morphological characteristics of the shoots were measured. We would like to ...
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### Random effects in repeated-measures design using lme

I have a repeated-measures design where participants were measured 4 times each on 2 consecutive days. There were 2 conditions, randomly attributed to day 1 and day 2 for each participant. So, this ...
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### How to address a detected nesting structure using emmeans

I'm analysing the results of a M BACI experiment. When trying to estimate means using emmeans, I'm getting this message: NOTE: A nesting structure was detected in the fitted model: BurnType %...
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### diagonal var-cov matrix for random slope in lme4

I am fitting a mixed effect model with a random slope on a factor with 6 levels using the function lmer(). ...
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### Repeated measure for multinomial logistic GLMMs in SPSS?

I am analyzing some linguistic data, where each subject has to rate the acceptability of a number of sentences on a scale of 1-7. I am running a Generalized Linear Mixed Model in SPSS, with a ...
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### Model is nearly unidentifiable: very large eigenvalue

I'm fitting a generalized linear mixed model using glmer() and I'm getting a warning that I don't understand: ...
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### Is it proper to compare a full linear mixed effect model that converges and an refined model that does not?

I was trying to construct in Rstudio a full LME model and a refined one (full model minus one predictor) and using anova() to get the main effect of the dropped predictor. My full model converged (but ...
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### How to set up Linear mixed model in SPSS? [duplicate]

I am trying to find out how inflammatory markers change in response to a mechanical device change. I have daily readings for the 5 days before the event and for the 5 days after the event. I am ...
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### Linear mixed effects model for trial [R]

I have finished a trial where we measured continously measurements like blood pressure ...
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### Comparing fixed intercepts of different mixed models R

Given 3 variables: y is continuous, x is continuous, z is a repeated measures factor, nested within subjects. I have two models from different data sets a and b: fitm1 <- lme(y ~ x + z, random = ~...
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### How is it possible to control for observer bias in measurements with a random effect?

I have a dataset with repeated (but not always) measures of animals. I need to control for observer bias in measuring the morphology of my animal. I'm wondering what is the way to first estimate ...
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my data: ...
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### Data transformation on grouped data

I am running an Ax(BxCxS) mixed design. During data screening, I assessed for normality by splitting my data based on the two levels of Factor A. Some variables for one level are nonnormal (and normal ...
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### Stats questions for a laboratory experiment with a small number of animals

I've been asked to run the stats on an animal behaviour experiment performed in a laboratory setting and, coming from a field ecology background, I have some basic questions regarding how I should ...
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### 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, ...
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### A non-linear regression model for within subject observations

I am trying to perform the equivalent of a repeated-measures ANOVA using data that have a non-linear relationship. There are two independent variables: Spacing between stimulus (10, 20, 35, 45, 60), ...
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### Repeated measures in a mixed model

I'm trying to fit a mixed model for data from different medical centers, where "center" is thought of as random. I have data over 2 years on how many patients they receive each day. I have several ...
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### Estimate Particle Density from Image Analysis

Suppose I have an old image of an object where the objective is to estimate the mean particle density of said object. Using a software called ImageJ, I am able to run a thresholding algorithm to ...
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### In glmer, can I treat both like a random effect and a fixed effect the same factor?

I conducted a memory study and used glmer to find if there was an interaction between time and ...
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### Repeated measures/pseudoreplication - Comparing all samples against all other samples

I am currently analysing some data, and I am not confident that I am going about it in as statistically sound way. We are trying to determine whether our treatments affect the distance between two ...