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# 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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### Calculating sums of squares for mixed-model ANOVA

I'm trying to get an understanding of how to calculate the sums of squares values in a mixed-model ANOVA (mathematically, not just the syntax for R or SPSS!). I've been trying to figure this out for a ...
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### Likelihood Ratio Test & Bootstrapping for testing significance fixed effect Linear Mixed Model

Data: I have a continuous nested outcome (measurement) and two categorical predictors (X1 is a grouping variable; X2 is a time variable "Day" with 5 categories) and their interaction. The nesting is ...
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### If I z-score all continuous variables of a linear mixed effects model, can I report the beta weights of the fixed effects as r values?

I have model that looks something like this ...
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### Estimate random effects for a new individual with a linear mixed effects model

Consider repeated observations $\mathcal{Y} = (y_{i,j})_{i,j}$ obtained for $p$ individuals ($1 \leq i \leq p$), at different time points $t_{i,j}$ $(1 \leq j \leq n_i$). The "random slope and ...
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### inconsistent results in two-way repeated measure analysis using mixed models

I have two factors: interval with two levels, and spd_des with three levels. Each of the subjects (grouping variable ...
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### How to compare model coefficients from models with different distribution family and link functions

I am trying to understand if I can compare two models with different family distributions / link functions directly, or if this does not make sense mathematically. In my example, I am measuring some ...
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### Should I use multilevel modeling? One between-subjects continous predictor, one within-subjects categorical predictor

I have recently collected my dissertation data. I would like to know if I should use multilevel modeling to answer my research questions. Here is a brief summary of my method: Participants (n = 392 ...
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### couldn't get the names of levels of random effects in R [on hold]

I'm trying to print the "between-event residuals" (which is the conditional modes of a random effect) from a mixed effects model to a .csv file. The thing that I couldn't get is, length of ranef ...
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### Linear mixed effect model : formula and difference between random effect and within subject effect [closed]

I want to explain the variablity of my continuous dependent variable a with two independent variables: one between subjects variable ...
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### How to do statistical analysis that include 2 levels of repeatedness in R? [on hold]

I know this question is a bit general, I don't have and reproducible code to share, since it's a general question, I'm trying to understand where to start the investigation about it: I would like to ...
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### Interpreting the intercept of a Linear Mixed Model Results in Python - Statsmodel Package

Using python package statsmodel and the code in this link: If a linear mixed model has a random variable with x groups. then why when one would run this code: ...
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### Mathematical notation (or formula) of mixed effect models

I am unsure how the correct mathematical notation of two mixed model I've estimated in R should look like. The data consists of test scores of students that were in different classes. Some of the ...
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### Should I use contrast coding( or any specific coding) for factor predictor (condition) with 2 levels : “treatment” & “Control” in brms & lme4?

This is for hypothesis testing where my hypothesis states that the dependent variable has a higher value in the treatment condition. I'm doing it both in brms & lme4 to do a comparative study ...
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### problem calculating the intercept manually in a linear mixed effect model

When I run a linear mixed effect model on this dataset, the intercept coefficient does not equal the mean of the marks where the other variables are 0. ...
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### Does random effects account for covariates not included in my regression model?

I am using a (Bayesian-based) mixed-effects regression model that incorporates both fixed effects and random effects.I have 3 fixed effects/covariates: 1) employment rate 2) crime rate 3) home ...
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### R: linear algebra representation of the prediction operator for a mixed effects model

(See edit at the bottom for the bounty) I am trying to learn how to simulate LMM data with matrix linear algebra. So far I've managed to simulate a simple model with a random intercept: ...
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### How to do principal component regression for repeated measures?

I have between-subject repeated measures data. I want to select the parameters for my regression model. PCR /PCA is one option to reduce dimensionality. How can I do this in the case of a repeated ...