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Questions tagged [random-effects-model]

Parameters associated with the particular levels of a covariate are sometimes called the “effects” of the levels. If the levels that are observed represent a random sample from the set of all possible levels we call these effects "random".

Parameters associated with the particular levels of a covariate are sometimes called the “effects” of the levels. If the levels that are observed represent a random sample from the set of all possible levels we call these effects "random."

Reference:

Bates (forthcoming). lme4: Mixed-effects modeling with R.

1381 questions
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How bad is considering a random effect as a fixed effect?

In an experiment with 5 technicians from different companies, we investigated effects of new equipments. The interested response variable is categorical. One thing I am considering is that the technician effect is a random effect. But it's hard to…
Tae-Sung Shin
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Why is the variance of my random effect negative?

I have two variables, response and group, and I fitted the model in which group is a random effect. proc mixed data=myData nobound; class group; model response =; random group; run; However, SAS returns a negative variance for the random…
user7064
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How do we interpret the coefficients of the random effects model?

Also, what is the difference between the interpretation of the coefficients of random and fixed effects? What I understand is this: in fixed effects, the coefficient of x shows that, what would be the increase in y, as compared to individual i's own…
kbhavni
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Fitted values of a random effect model

I have this model: $$v_{ij} = 1 - x \beta + \delta_i + e_{ij}$$ where $\delta_i$ is the i-th random effect, $e_{ij}$ is the usual error term. I have obtained the betas and now wish to derive the fitted values. How could I do that? Do i need to…
Günal
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Covariance structure for random intercepts and slopes

Can you please help me figuring out what the covariance structure of a model with random intercept and random slope is? Here is my model $Y_{ij} = \beta_0 + \beta_1 t_{ij} + b_{0,i} + b_{1,i}t_{ij} + e_{ij}$ where $b_{0,i}$ and $b_{1,i}$ are random…
user48405
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'random intercept only', 'random slope only' and 'random intercept and slope' models

I have a terminological question about the use of the terms random intercept models, random slope models and random intercept and slope models. Through my readings, I find that most authors use the terms random slopes, and random intercepts and…
Shad
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Random effects vs fixed effects with balanced designs

In my statistics lectures it is mentioned that for balanced data (same number of participants in each block), the results will be the same whether the model is fitted with factor A as a fixed effect or a random effect. For example: lme(effort ~…
Tal Bashan
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Linear Model vs Random Intercepts Model

Suppose we fit a linear model $$y_{i}=\beta_{0}+\beta_{1}x_{i}+e_{i}$$ where $e_{i}\sim N(0,\sigma^{2})$. Suppose we also fit a random intercepts model $$y_{ij}=\alpha_{0}+\alpha_{1}x_{ij}+u_{j}+e_{ij}$$ where $e_{ij}\sim N(0,\sigma_{e}^{2})$ and…
Kian
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hierarchical linear model with moderation in R

Could someone please check if my model fit is correct??? Thank you!!!!!! Here is the background: participants fill out one baseline survey and seven identical follow-up surveys during a week. I have a variable BN in the baseline, DN and DE in the…
Yan Iris
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Correlation among Random effects. How does it affect the estimation of variances?

I have a hard time trying to understand what is the meaning of the correlation among random effects and how it affect the estimation of the variances of random effect and predictions. I work with genetic effects and there is a negative correlation…
marb_021
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Treatment mean comparisons in a mixed model with random and fixed effects

I have run a mixed model with one random effect, one fixed effect and a second order covariate effect. The random effect models the individual experimental units in my study. The LSMeans calculated for each experimental unit from the full model are…
mattjay
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Why does adding a covariate of age cause variance of random slope (log time) to increase?

Why does adding a covariate of age cause the variance of random slope (log time) to increase? Isn't it supposed to decrease when a covariate is added? Firstly, there is only $log(time)$ in the model with random intercept and random…
user1421972
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Applying random block in LME

New to LME's and wondering if someone might be able to help me with this question. Does the application of a random block in an LME apply to both the dependent variable and the independent variable(s)? For instance if my model is: mod <-…
nordic5
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3 levels model with random slope in R

I'd like to estimate a 3 level model (years clustered in districts clustered in counties) on the Leyland data (Mortality in England and Wales, 1979-1992 An Introduction to Multilevel Modelling using MlwiN) using R. I have 3 predictors (year79 (at…
elisabetta
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Random and fixed factors

In my masters work I want analyse whether a treatment with a specific drug changes a specific physiological response (dependent variable) in rats. However, it needs be stimulated so I can compare the magnitude of the response between the groups…
Igor Simões
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