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

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11 views

Experimental design and mixed models

I want to test effect of 3 PH on larval development. I would like to know what is the best experimental design and statistical analysis. We can only use 3 compartments of sea water, each one with a ...
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28 views

Multivariate model in lme() with independent random effect, similar to MCMCglmm

I would like to specify a multivariate model with lme with a random effect for group which is independent across variables. I found this post, which explains that ...
3
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38 views

Mixed effects modelling; what to do when model is over-specified?

I'm trying to use mixed-effects modelling to analyse some data. There are a number of variables that I need to specify within the model, two of which are between-participants (...
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0answers
12 views

Fitting a Mixed Model with Random and Repeated effects in SAS

I have want to fit a linear regression with repeated measures and random effects. The data come from clinical observations. In CT images The dependent variable is the diameter of a lymph node lesion ...
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2answers
50 views

What is the right way to analyze a nested design in R?

I know that there are already a host of questions about nested designs but many of them haven't been answered or come from biological domains which I sometimes find hard to transfer to my domain. I ...
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0answers
24 views

Demand Forecasting : Montecarlo Simulation

I am trying to build a demand forecasting model for human resource team. I have thought of using monte carlo simulation method to do it. Is it the right technique for it? Has anyone used it to ...
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0answers
22 views

How to do a power analysis for an unbalanced mixed effects ANOVA?

I need suggestions for how to calculate the $n$ required for 80% and 90% power for >30% change from baseline ($T_0$) at $T_1$ or $T_2$, drug vs. placebo, 2:1 ratio; 20% CV in test; factors: subject, ...
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1answer
47 views

How to compare models from different but related datasets?

I'm building regression models on four the different but related data set and at the end, I want to test the significance of models. Since my models are built in a different data set, it's not ...
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0answers
28 views

How to model non-linear time courses with nlme

I have some time course data which plotted looks like this: I am trying to fir a model to it using nlme.lme(). I am interfacing with R via RPy, and using the ...
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22 views

How to apply the random statement in my model?

i am trying to model the following data in SAS using proc glimmix and i would like feedback if i have modelled my data correctly. My data consist of individual chickens (ID) who are grouped by ...
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1answer
34 views

Repeated-measures, crossover analysis using linear mixed model in R

I have a data set that I am attempting to analyse in R and I am relatively new to the environment. My full data set contains 7 subjects (represented by Subject), that all receive 3 treatments ...
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1answer
35 views

The 'best' model selected with AICc have lower $R^2$ -square than the full/global model

I have used the R lme function (nlme package) to construct linear mixed models, with a single random effect (as a random intercept) and a varIdent variance structure on a fixed effect (that is a ...
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1answer
79 views
+50

Relationship between paired t test and simple mixed model

I have a psychological data set which, traditionally, would be analysed using a paired samples t test. The design of the experiment is $39 (subjects) \times 7 (targets) \times 2 (conditions)$, and I'm ...
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0answers
25 views

Proc Mixed statement

Suppose I have a data set: ...
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0answers
44 views

Help with lmer in the lme4 package

I am new to using linear mixed models and would greatly appreciate any help I can get. I have an equation of the form $ y = X\beta + Zu + \epsilon$ where $u$ is a random effect whose covariance ...
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0answers
24 views

Understanding repeated covariance types in SPSS?

I am working in SPSS on a repeated measures linear mixed model and I am having a really hard time wrapping my head around how to select a "repeated covariance type". The options are: ...
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0answers
10 views

How to get/calculate confidence intervals for slopes of the continuous*categorical interactions?

Not sure if this should be in Stack Exchange or here, but here goes. I have a linear mixed model in SPSS, and I want the confidence intervals for slopes of the continuous*categorical interactions. ...
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0answers
23 views

How to perform a meta regression with a random effect model?Which model should I use?How to start? (beginner)

I have to perform a meta-regression, using mixed or random effects model, but I don't have any software (except Matlab) and I'm new on this topic (having a relativelly poor statistics background). ...
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29 views

Within-subject and between-subject fixed effects in mixed model

I've been trying to analyze some data using mixed models but I have some troubles to understand how should I include both within-subject and between-subject fixed effects in such models. Let's ...
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0answers
8 views

Negative Binomial Mixture in PyMC [migrated]

I am trying to fit a Negative binomial mixture with PyMC. It seems I do something wrong, because the predictive doesn't look at all similar to the input data. And the predictions for the parameters ...
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0answers
33 views
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22 views

MANOVA for mixed model with multiple repeated measurements

I struggle performing a MANOVA for a mixed model. I have the following columns: S - subject (1,...,N) B - in between group (B1, B2) W - repeated measurement - within (W1, W2) M - measured dependent ...
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0answers
19 views

How to model a multiplicative effect of a parameter

I am having difficulty in fitting a model on data. Basically, I have data about the evaluation of phenotypic property (i.e. hard) of 65 palm trees by 5 judges. As an evaluation scheme, each judge ...
4
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1answer
69 views

Longitudinal item response theory models in R

I'm trying to fit longitudinal item response theory (IRT) models in R. I have a test that was administered at multiple measurement occasions. I'd like to examine individuals' growth curves of factor ...
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0answers
12 views

Modeling paired data: Philosophical difference between using mixed effects model and using grouping-variable-level outcome

I am facing a problem of detecting change in infection rate after surgery in about 400 eye surgery patients. Crucial medical background includes the following-- About 30% patients have both eyes ...
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1answer
38 views

Interpreting the mathematical formula of a mixed effect model

I am a bit confused about the function of a parameter in setting up a linear mixed effect model (hierarchical/multilevel model). This is how I understand a (random intercept and slope) multilevel ...
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0answers
6 views

MLR equivalent for repeated measures, multiple correlated responses

I'd like to determine the best approach to determining effect sizes for a set of experimental data with multiple correlated responses. Due to repeated measurements and high correlation between ...
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2answers
76 views

mixed model: is it primarily used for prediction or explanation or both?

Inspired by this post on the difference between explaining and predicting. I want to ask is mixed model primarily used to get better explanation (such as, but not limited to, getting better ...
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40 views

Comparing slopes in mixed-effect model

My data looks like the attached picture. The dependent variable indirectly measured physical activity. I tried to use mixed-effect model rather than RM Anova, because my actual data is imbalanced. ...
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0answers
14 views

Site effect in GAM model

I am trying to build GAM model to see the effect of several environmental variables on the total abundance of one species. I have collected samples from three sites with three replicates from each ...
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0answers
25 views

repeated measures ANOVA - non-experimental data

For every year, for eight years, I have a set of projects (n=332). The number of projects that exist in each year varies (for example, some years there are 10 projects others there are 60). In each ...
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1answer
37 views

fitting LMEMs for repeated measures with no correlation between intercept and slope

For a simulation study, I contrast the power of different LMEMs for repeated measures. To get p-values, I use likelihood ratio tests where I compare a model including a fixed treatment effect with one ...
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0answers
21 views

Testing the random slope with correlated random effects

I have a mixed/random effects model $$\mathbf{y}_i=\mathbf{X}_i\boldsymbol\beta+\mathbf{Z}_i\mathbf b_i+\boldsymbol\epsilon_i,$$ where random effects $\mathbf b_i$ has variance-covariance matrix ...
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0answers
13 views

Choosing levels of random factor in a mixed model

My apologies in advance if this question is as much about experimental design as it is about statistics. I'd like to know if there is a "best" way to choose levels of a random factor in a mixed model. ...
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17 views

Split plot ANOVA or t-test

I did a study in which I wanted to see if a teaching intervention would have an effect on student learning. I nonrandomly divided students into two groups, a control and experimental group, and gave ...
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1answer
35 views

Hausman's test for all $\beta$s – comparing FE vs RE models

I fit several two level models in SAS using PROC MIXED: an empty model with multilevel structure (null), a model with a level 2 covariate (partial model), and a ...
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1answer
68 views

Random factor nested in two fixed factors

I have read Random effect nested under fixed effect model in R, but I have a doubt: My data is on germling survivorship, I have Temperature as a fixed factor (2 ...
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1answer
27 views

Fitted values of 'lme' function result

I fitted a linear mixed model with R as follows. ...
1
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1answer
41 views

SAS Proc Mixed model interpretation

I'm fitting a linear mixed model by SAS. There are 596 sectors and 8489 subjects. (each sector contains 10~15 subjects). Each subject is measured at most 6 times, so the total number of observation is ...
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0answers
24 views

MIXED modeling of 2 within-subject factors with 2 repeated factors and df

This is a novice question regarding MIXED models, denominator freedom degree, and long format (e.g., in SPSS). Most Mixed Model tutorials that I find address between factors and repeated measurments. ...
2
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1answer
56 views

Multilevel modeling: longitudinal data with within-subjects factors

I have a data set with experimental data that I am analysing with multilevel modeling. Data are structured as follows: 24 Sessions 6 Subjects per Session 10 Rounds per Subject There was one ...
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0answers
28 views

How would you model this random effects structure?

I have a sort of weird and complicated model design, and I'd like to get your opinion on how best to model the error structure. I have 100 sites, with each site falling into 1 of 4 different forest ...
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0answers
46 views

Alternative to MANOVA when group covariance matrices are heterogeneous?

I'm running into problems meeting some of the assumptions of MANOVA, namely homogeneous group covariance matrices and normality. I'm looking for an alternative approach where assumptions are not ...
0
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0answers
11 views

Parameter estimation of LMM with multiplicative measurement error in fixed co-variate - How?

I have a linear mixed model, with multiplicative measurement error on the fixed co-variate only (i.e. the random part is assumed to be measured without error). How could I best estimate the ...
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0answers
50 views

Model selection on variance parameters (and about REML)

Various descriptions on model selection on random effects of Linear Mixed Models instruct to use REML. I know difference between REML and ML at some level, but I don't understand why REML should be ...
2
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1answer
77 views

Difference between log-normal distribution and logging variables, fitting normal

Context: I have a set of data that is bimodal, so I used the mixtools package in R to fit a bimodal normal distribution to it. It looked as if the normal did not fit very well, and given other similar ...
2
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0answers
27 views

When using the MIXED procedure in SPSS should set my 'time' variable as scale or categorical?

I currently have a modelling issue, specifically in determining how to code the 'time' factor in my analysis, when the DV has already been adjusted for age. My DV is a measure of child development, ...
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0answers
89 views

Post-hoc tests on linear mixed model give mixed results.‏

I am quite new to R so apologies if I fail to ask properly. I have done a test comparing bat species richness in five habitats as assessed by three methods. I used a linear mixed model in lme4 and got ...
2
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2answers
128 views

Why is a Mixed model a non-linear statistical model

I was wondering if anyone could elaborate more on this statement which I came across whilst reading a book on non-linear mixed effects model. I know that you can have linear, generalised linear and ...
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1answer
144 views

Coefficients from glmer in R

In a mixed effect model where the intercept is random effect and the slope is fixed effect (see the code below), I understand the output of summary(glmer(...)). But ...