# 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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### Putting the following linear mixed effect in matrix notation

I am used to seeing the linear mixed-effects model in the form: $$Y_{ij} = \mu + \alpha_i + \gamma_j + (\alpha\gamma)_{ij} + \epsilon_{ijk}$$ assuming $\gamma_j i.i.d \sim N(0,\sigma^2_{\gamma})$ ...
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### Additional steps for smoothing log transformation to establish RMSE? [closed]

A GMLE is too complex for the data, so I use a LME and have a log(DV + 1) ~ IV. If I want to calculate the RMSE, would it be principled to subtract 1 from all modeled values, then exponentiate these, ...
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### lme models: checking assumptions and transformation for non-normally distributed residuals?

I have an model, specified as follows: ...
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### Linear mixed model with many NAs

I am running a linear mixed effects model in R using the lmer4 package. I was wondering if my data is structured in the right way for this purpose. In a few words I have a response variable "...
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### Single Observation with Some Groups. Multilevel model or other analysis?

I am having trouble determining which method to use to analyze my data. Here is the info: -575 observations nested within 292 groups -some groups only have one observation, the max number is 23 in a ...
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### How to do logistic mixed regression with these data?

In this study, measurement was done on each subject at 3 time points (0, 4 and 80 hours). Each subject was then checked for some event. The data is in following form: ...
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### Parsimonious Mixed Models

I recently read a paper on the trimming of random effect structure by Bates, Kliegle, Vasishth and Baayen (2015). My understanding is that the Parsimonious Mixed Model they proposed mainly follows the ...
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### Mixed model for trial-based analysis

I conducted an experiment that investigated preferences for two-digit numbers. Each digit was randomly drawn from a list of digits between 1 and 9, with one digit presented at a leftish position and ...
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### Converting Cohen's $F^2$ to Cohen's $D$

How can I convert Cohen's $F^2$ to Cohen's $D$? I am interested in calculating the effect size for the difference between two groups in a mixed model. The data is from a within-subjects experiment ...
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### Using RMSE and AIC to compare three separate “final” models (one with double observations)?

I'm looking at three models (linear mixed effect) looking at crime. The first looks at total crime so there are ~96000 observations. In the second model, I look at crime as a function of crime type (...
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### Obtaining p-values in a robustlmm mixed model via Satterthwaite-approximated DFs of the equivalent lme4 model?

I've used lme4 to fit a mixed model and could obtain p-values by using the lmerTest or afex packages. However due to heteroskedasticity (Levene Test) I also fit a robust model (rlmer command in the ...
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### How do I interpret this hurdle model summary (pscl)?

A little bit about my data: I have four treatment groups: control, early, late, both. For each group, I counted nymphs and eggs on leaves on five different dates. The design is randomized complete ...
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### How do I interpret results of a mixed effect linear regression with 7 independent variables accounting for variability of one dependent variable?

I have 7 moderators while fitting the mixed effect model using the metafor package, my results show many interactions and I am a bit confused on how to present ...
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### Mixed Effects Logistic Regression w/ Repeated Measures for Observational Data

I am working on a study of how different scholarship programs at a university may influence student retention (i.e., if students are still enrolled at the university one year later). Each student can ...
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### Problem with non-normal residuals (lmer function)

I work with animal personality and I am trying to analyze individual differences in response to certain stimuli. Taking this particular dataset as an example, I am analyzing how much distance animals ...
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### generalized linear mixed models vs linear mixed effect models

What is the difference between generalized linear mixed models, and linear mixed effect models (lmer function in package lme4) in terms of distributions of the response variable? Do they both work ...
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### How to export a formula from a SAS model

I am a bit of a SAS novice so please forgive my ignorance. I have a generalized Linear mixed model in SAS based on past data but I don't know how to export it to a pure mathematical formula that ...
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### Relevance of Mixed Model Estimates vs. Observed Means [duplicate]

This question is a follow-up to a previous question I asked regarding mixed model effects construction, linked here. It provides some background, although this is a broader question with little to do ...
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### OLS or GLS for balanced random coefficient model [closed]

For the balanced random coefficient model, The beta_hat is the GLS for beta, would you please help me to figure out that why it is Y_bar, where does y_bar come from. Thanks!
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### 'Translate' ANOVA comparison on regression parameters into linear mixed model

I am analysing data from a medication study. Participants did the same task twice; in one session they were given a certain drug and a placebo in the other one. The order of the sessions was perfectly ...
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### three way interaction in lmer

I have two continuous variables (cfreq, and LanPro), and one catergorical variable (cond_aud, as shown in the picture). The summary of a lmer model shows a three way interaction of aud (EA and NoA) x ...
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### Power calculations for a mixed model using simr

I'm trying to conduct a power calculation for a mixed effect model I built using lmer. I already have some pilot data, so I have an idea of the estimated effect size, but what I'd like to know is what ...
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### How to enter confounding variables and variables competing for exposure into a mixed-effects model in lme4?

Let's imagine I am interested in the association between happiness and pain. I run a study where I ask participants to rate both ...
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### Comparing variables against a baseline in R random effect mixed models

I am trying to analyse the effect of age and town on F2 value of speakers. Firstly apologies if this question is really basic, I missed pretty much all of my R tutorials due to the pandemic and having ...
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### Redundant Parameters in Cross-Level Interaction: Mixed Modeling

I'm using SPSS to run a Mixed Model with two categorical (factor) predictors with an interaction between the two predictors. I get the following Estimates of Fixed Effects: In the interaction I am ...
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### Two levels of a factor in a linear mixed model; one is fixed and another is random. Is that possible?

Can you specify one level of a factor as fixed and the other as random in a linear mixed model (with lmer)? Some background information first: A set of speakers who vary in their proficiency levels (...
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### Linear Mixed Effects Models: how to model dependent categorical variable?

I am trying to fit a linear mixed effects model with several fixed effects and a random intercept that varies per subject. My problem is that I know that one of the fixed variables, let's call it 'A'...
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### Linear mixed effect model in statsmodel package

I try to use linear mixed effect model in Python statsmodels package. However, I have no idea how to conduct and interpret the result. Group 1 (20 people) : base line & follow up Group 2 (20 ...