Tagged Questions

Refers to a class of models developed to account for correlation that may occur within nested data.

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12 views

Repeated measures ANOVA and uneven number of trials

Suppose I have multiple responses from each subject in three different conditions (A, B, C). If I would decide to run a repeated measures ANOVA, I would first average over the repetitions from each ...
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1answer
55 views

Unified view on shrinkage: what is the relation (if any) between Stein's paradox, ridge regression, and random effects in mixed models?

Consider the following three phenomena. Stein's paradox: given some data from multivariate normal distribution in $\mathbb R^n, \: n\ge 3$, sample mean is not a very good estimator of the true mean. ...
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1answer
32 views

Extracting slopes for cases from a mixed effects model (lme4)

I would like to extract the slopes for each individual in a mixed effect model, as outlined in the following paragraph Mixed effects models were used to characterize individual paths of change in ...
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1answer
34 views

estimating LMM with r

Suppose I have a model $$\begin{bmatrix}y(1)\\y(2)\end{bmatrix} = \begin{bmatrix}\mu \\ \mu \end{bmatrix} + \begin{bmatrix}\Lambda \\ \Lambda\end{bmatrix} + \begin{bmatrix}\varepsilon(1)/\rho_1\\ ...
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6 views

Proc Mixed for a random slopes model - contrast the slopes?

I have a need to make predictions about a set of students $^1$ who are nested under teachers, under schools, under districts. I have produced the below model, and I now wish to do some forecasting at ...
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1answer
36 views

Using the same variable as a fixed and random effect in Mixed Effect Models

The experiment this data comes from an experiment where two people collaborate to put objects in a specific order. The Direction has the target array on their screen, and the Matcher has a scrambled ...
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0answers
20 views

Assumptions for nlme

I want to analyze a repeated measure design with two independent variables (var1, var2) where the subjects had to solve three ...
2
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1answer
39 views

lme4: profile takes lot of time for a complicated model

I have a pretty complicated mixed model (cross classified data) and a pretty large dataset (>700000 obs.). The lmer function took few hours to compute, but profile takes over two days and is still ...
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0answers
12 views

Standard errors of estimates in multi factorial LMEM

This question may already be well-answered as it seems relatively straight forward, but my search of existing posts has failed... apologies if it is redundant. I am building a linear mixed effects ...
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0answers
11 views

G and R matrices in mixed model and model selection

I have data in which the plants were subjected to four conditions and measured weekly for a month. I would like to incorporate "plot" as a random factor into my linear mixed model using SPSS. I am ...
2
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0answers
18 views

Data analysis : replication, pseudoreplication and mixed models

I have several questions concerning analysis of data, especially when there are replications and/or pseudoreplications. First, I read an example in « pseudoreplication is a pseudoproblem » where we ...
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24 views

mixed effect regression model

I would like to expand over a previous question of mine (What is the correct model for this experiment design?), with slight modifications... To set up the scene : We have a completely randomized ...
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0answers
32 views

Determine the causes of change in time with mixed models

I have a database with several continuous variables measured in two times. I searched for a change in time in my dependent variables in this way: ...
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0answers
24 views

Assumptions of Linear Mixed Model

I had data with repeated measurement and nested design. Conventional ANOVA requires strict control on homogeneity of variance and repeated measurement ANOVA requires assumption of sphericity. ...
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1answer
39 views

ANOVA - when homogeneity of variance is violated

My data was a repeated measurement (3-4 measuring times) with one fixed factor (4 doses) and nested (Please find an example below). I would like to ran ANOVA but the assumption of homogeneity of ...
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0answers
10 views

Error using “cengaussian” family with MCMCglmm

I'm trying to run a model using a cengaussian family distribution with the function MCMCglmm. The model is: ...
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0answers
31 views

How can I model this problem?

Genetic algorithms are a kind of evolutive approach to problem solving where solutions are randomly generated and crossed with each other as to produce other solutions. With each generation or ...
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1answer
131 views

What is the meaning of $\oplus$ and $\otimes$?

I am struggling to fully understand some notation in a book where they use a "crosshair" symbol - first like $\bigoplus\limits_{i=1}^n{} Z_j $ where the $Z_j$ are matrices and second like $I_n \otimes ...
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0answers
10 views

How to take care of the percentage/rate of an absolute number as independent variable?

I am working on a mixed model, where suppose I have several stores of different sizes. The number of products manufactured in each store is different, say one store can manufacture 100 and other can ...
2
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1answer
78 views

Mixed effects model with repeated measures

I was trying to work out this on my own but I find myself overwhelmed. I am looking at the amount of moisture present in forest fuels (FMC) following forest thinning. Forest fuels are classified by ...
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0answers
23 views

Correlations of fixed effects in logit mixed model with a nested fixed effect

I am using lme4 in R to fit a logistic mixed effects model of psycholinguistic data with three categorial (binary) fixed effects and two crossed random factors (subjects; items). The critical ...
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0answers
8 views

Testing hypothesis about the location of the maximum point on a curve

I have data from an experiment on the relationship between PPI (the dependent variable, a measure of startle reflex attentuation by weak stimuli) and SOA (the main independent variable; it's the time ...
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2answers
97 views

Getting P value with mixed effect with lme4 package

I have problem with getting p value from my mixed model, library(lme4) ...
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1answer
40 views

Linear regression or mixed effects models for data with two time points?

I have a dataset in which individuals were assessed at two time points during the study on a cognitive test, as such I was wondering which statistical model would be more appropriate for my data, ...
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1answer
36 views

Does it make sense to add random coefficients to a fixed effects (fixed-intercepts) model?

If you have panel data, and you fit a model like $$ y_{it} = \alpha_i + X_{it}'\beta + \epsilon_{it} $$ then you have $E[\hat\beta] = \beta$ if you can make an argument that $E[\epsilon]=0$. This is ...
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1answer
91 views

Summarizing and plotting several combined relationships with LMER

I want to see if there is a significant relationship between predictor and value. I've measured these two variables in 6 different conditions (not a full 3 x 3 design because feature1 and feature2 ...
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0answers
15 views

Longitudinal design: how to take into account baseline measures

I have a (small) data set of 15 subjects randomly assigned to one of two groups. All subjects were measured at 7 time points. Ideally, I would like to answer if the groups differ at certain time ...
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2answers
47 views

How to interpret a negative correlation of random effects in a mixed-effects model (in R)?

I've just gotten stuck in interpreting the output for a linear mixed effects model. My model includes Week as a time predictor, and scores on a depression scale as outcome. I have not worked with R ...
2
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1answer
63 views

What is the lme4::lmer equivalent of a three-way repeated measures ANOVA?

My question is based on this response which showed which lme4::lmer model corresponds to a two-way repeated measures ANOVA: ...
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0answers
25 views

Check homogeneity of variance for linear mixed model in spss

I ran a linear mixed model (LMM) for my nested data and would like to check for the homogeneity of variance assumption. As there is no a button for checking the homogeneity of variance at the LMM ...
4
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2answers
51 views

Comparing between random effects structures in a linear mixed-effects model

During a recently asked question about linear mixed-effects models I was told that one should not compare between models with different random effects structures using likelihood ratio tests. Up until ...
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0answers
11 views

How to model non-linear, linear and crossed random effects in one model

I have a model with fixed and crossed random effects like this: glmer(response~1+var1+var2+var3+var3^2+(1|var4)+(1|var5)+(1|var6), family="poisson") Now, I decided that variable3 is best modelled ...
0
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2answers
62 views

How to report a linear mixed-effects model equation

I have run a linear mixed-effects model, with one fixed effect (dd) and a random slope and intercept term for individual (fInd) and would like to know how to report the results? In particular, I would ...
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0answers
26 views

Joint Models vs the 'usual' time-dependent Cox regression for time-varying predictors

I've got a methodological question, and no data set attached. Suppose I aim to fit a proportional hazards model (Cox) for survival data. I have multiple observations for each individual (data in long ...
0
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1answer
23 views

longitudinal dataset with multiple binary dependent variables

I have a dataset where a test (a continuous variable) is administered every 3 months for 2 years for most of the participants (approx 25% have one or two missing scores). There are further ...
13
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1answer
191 views

Invalid inference when observations are not independent

I learned in elementary statistics that, with a general linear model, for inferences to be valid, observations must be independent. When clustering occurs, independence may no longer hold leading to ...
2
votes
2answers
83 views

comparing non nested models with AIC

say we have to glmms mod1 <- glmer (y ~ x + A + (1|g) data= dat) mod2 <- glmer (y ~ x + B + (1|g) data= dat) These models are not nested in the usual sense ...
5
votes
2answers
176 views

Can correlated random effects “steal” the variability (and the significance) from the regression coefficient?

I have time-series count data $N_{i,j}$ (population sizes in site $i$ and year $j$) and I want to correlate year-to-year changes with the environmental conditions $x_{i,j}$. For this, I am fitting ...
0
votes
1answer
25 views

R- predict payment day (1-31)

I need to predict payment day of the month (1-31) for each client (I have at most 9 month of payments and on average is 5). I have both categorical variables and numerical. I tried to use rpart to do ...
0
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0answers
29 views

Two-way Repeated Measures ANOVA with replicated measures

My experiment involves 16 participants with a dependent variable (PP) tested under 2 conditions, across 3 different time-points. At every time-point, each participant is tested twice. My data is ...
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0answers
29 views

Variance functions and transformations in linear mixed models, beginner questions

First post here. I'm pretty much a newbie both in statistics and using R, but nevertheless trying to fit a linear mixed model with the package nlme. My question is about transformations/variance ...
3
votes
1answer
42 views

How is it meaningful to give fitted values for random effects if they don't appear in the likelihood function?

Software for fitting random effects models tends to output values for the random effects. For example, suppose the model is $$y_i = \alpha_i + \varepsilon_i, \qquad 1 \le i \le n$$ where $$\alpha_i ...
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vote
0answers
55 views

High negative correlation between intercept and slope

I was trying to fit several mixed linear models, however for 2 (out of 4) I am getting quite strange results. The point is that I've collected data from two courses (a few students were the same in ...
0
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0answers
47 views

Random variables of mixed models

I am thinking about using mixed models as part of my research, but I am having trouble understanding its application. In particular, I have two somewhat related questions regarding mixed models. ...
0
votes
2answers
73 views

repeated measures ANOVA, crossover trial, R

I am sorry for stating such a question. Unfortunatelly, it's very-very hard to go through all statistics. I have a crossover study design with 3 treatments, 3 periods, and a baseline (covariate). The ...
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0answers
41 views

Intraclass Correlation Coefficient in mixed model with random slopes

I have the following model m_plot fitted with lme4::lmer with crossed random effects for participants (...
0
votes
0answers
51 views

Empirical Bayes estimates of fixed effects (STATA 12)

I want to calculate the empirical Bayes estimates of the fixed estimates estimated using xtmixed in STATA. I conceptually understand what it is trying to do, but I'm not sure how to implement it in ...
2
votes
0answers
49 views

Using a mixed effects regression model for between-subject design?

I have data from a between-subject experiment, where every subject was assigned to one of the two conditions, and completed varying number of trials (as much as they wanted). Number of trials is ...
0
votes
1answer
95 views

Estimation of school effects using xtmixed (in Stata 12)

I am trying to estimate school effects on student scores. I ran a model with student effects as a random effect and school effects as fixed effects as follows: ...
0
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0answers
14 views

Univariate fixed effect Vs Multivariate model -Negative Covariance, positive parameter estimate, but why?

I am trying to compare the results of two models. The first model looks at y with x as a fixed effect. The second looks at the covariance between x and y. Both models have repeated measures for x ...