# mixed effects model

1. ### [SPSS - Mixed Models] Repeated measurements data from randomised controlled trial

I am analyzing data from a randomized clinical trial, with 2 intervention groups (placebo and intervention) and repeated measurements over time. I am planning to use linear mixed effects modeling to analyze this longitudinal data and determine whether the intervention causes a change in response...
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### SPSS simultaneous equation models analysis with panel data

Hi to everybody, I've just created four cross sectional models based on panel data with MIXED MODEL procedure. Now I'd like to made a simultaneous equation models analysis. Do you know how I can do it? Do I need AMOS? And if yes, does anyone know whether there is a specific tutorial...
3. ### nlme arguments explained

Hi All, I'm trying to run an nlme on some data looking at the nonlinear response (in this case 'distance', but will also use for 'weight') of individuals ('possum') over time (repeated measures, recorded weekly for 12 weeks = 'week'). There were 3 different 'treatment' groups. Other factors...
4. ### Inoculated chickens-bacterial load. Non Linear Mixed Model with repeated measures?

:wave: Help! I have some data I am trying to analyze but was hoping to get some stats help with it. I'm not sure what the best way to analyze it is. I'm interested in seeing if there is any effect of different dietary treatments on bacterial colonization and shedding in experimentally...
5. ### [R - nlme] non-linear regression Michaelis-Menten model

Hello, I am attempting to model Michaelis-Menten uptake kinetics to predict denitrification rates (response) across a gradient of nitrate loading (predictor) in four seasons (June, August, October, and December) using a mixed effects model. The basic models run well in the nls program in R and...
6. ### mixed-effects models with (g)lmer in R and model selection

Mixed-effects models are wonderful for analyzing data, but it is always a hassle to find the best model, i.e. the model with the lowest AIC, especially when the number of predictor variables is large. Presently when trying to find the right model, I perform the following steps: 1) Start...
7. ### Multilevel model with crossed random effects - does this model make sense?

I have a complex design and haven't found similar examples online. I'd really appreciate any views on the way I modelled it. At a first stage, 19 editors improved the wording of 41 sentences - all editors saw all 41 sentences. At a subsequent stage, 3 judges assessed the quality of the edited...
8. ### Two-Level Model in Matrix Notation

A two-level model, with one explanatory variable at the individual level (X) and one explanatory variable at the group level (Z): Y_{ij}=\gamma_{00}+\gamma_{10}X_{ij}+\gamma_{01}Z_{j}+\gamma_{11}X_{ij}Z_{j}+u_{0j}+u_{1j}X_{ij}+e_{ij}\ldots (1) correlation between u_{0j} and u_{1j} is 0 . The...
9. ### "getVarCov" in lme

Is "getVarCov" of lme output gives variance-covariance of estimated "Standard Deviation" of random effects or variance-covariance of estimated "variance" of random effects . library(nlme) fm1 <- lme(distance ~ age, data = Orthodont) VarCorr(fm1) getVarCov(fm1) That is , VarCorr(fm1)...
10. ### How is to define the lme model syntax .

The following model assumes that the covariance between the random intercepts and random slopes across Subjects is Zero . lmer(Reaction ~ Days + (Days||Subject), sleepstudy) How can I write the same model by "lme" function under nlme pacakge assuming zero covariance between the random...
11. ### Specifying the variance component model "varComp" in R .

I am trying to fit a random slope model by "varComp" in R . For the following example , that is in "lmer" syntax , how can I write it in "varComp" syntax : library(lme4) library(varComp) fm1 <- lmer(Reaction ~ Days + (Days||Subject), sleepstudy) I am not understanding...
12. ### General Linear Mixed Model - how to run!

Hello, I need some help with how to run a mixed regression with a random factor please! I have a data set with 10 participants, who I conducted observations on multiple times (around 26 observations per participant), so in total I have around 262 observations. For each observation I have 2...
13. ### Interpretation of various output of "lmer" function in R

library(lme4) fm1 <- lmer(Reaction ~ Days + (Days | Subject), sleepstudy) The notation (Days | Subject) says to allow the intercept and Days to vary randomly for each level of Subject . Can you please explain me the result of the following commands ...
14. ### Calculating Non-Coverage Probability .

Hi , I have a two-level model with one explanatory variable (X) on the respondent level, and one group-level explanatory variable (Z) . I am following this paper http://joophox.net/publist/methodology05.pdf I am simulating data from the model . Three conditions are varied in the simulation...
15. ### Notation of Variance of Residuals in Multilevel Modeling

I am having some trouble to understand the notation of variance of residuals in multilevel modeling . In this paper "Sufficient Sample Sizes for Multilevel Modeling" , in p.87 below equation (3) , they mentioned " the variance of residual errors u_{0j} and u_{1j} is specified as...
16. ### Example of lmer() function in R documentation .

How is the following code working ? (fm1 <- lmer(angle ~ recipe * temperature + (1|recipe:replicate), cake, REML= FALSE)) In the formula of lmer : What does 1 before vartical bar , (1|recipe:replicate) , indicate ? How does "recipe:replicate" after vartical bar work ? I...
17. ### SAS GLIMMIX subject specific estimates

I am trying to analyze a dataset where each subject has 12 repeated measures (quarterly, over 3 years). I want to extract subject specific estimates of the time slope to evaluate if the subjects are changing significantly over time. The code I currently have consistently suggests that each...
18. ### MIXED model syntax - simple main effects

Hi! I am running a mixed effects models in spss and have found a significant interaction between session and sex. I now wants to examine the simple effects for sex and I've been trying the below syntax but keeping getting the following warning message: "The symbol sex was found following...
19. ### Correct way to dispaly the fixed effects of a mixed effects model

I have a question regarding crating a graph displaying the fixed effects of a mixed effects model that I cannot seem to find an answer to. I am not sure what the correct approach is. For example, when graphing a standard non-mixed effects model (i.e. binomial glm;logistic regression), I used to...
20. ### Linear Mixed Effects and interpreting transformations

Hi, I'm running a hierarchical linear mixed effects model in R (subject is nested in dyad). My dependent variable is a continuous variable. When I run the model I do not meet the assumption of homogeneity. A log transformation on the dependent variable does not work. However, when I use a box...