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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14 views

Is beta regression appropriate for this question?

I have a data set with death rate per 1000 birth as the response variable. The range of values for the response variable is [0.03 - 0.89]. The question to find association between death rate and other ...
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Equivalence of proc mixed SAS and R lme/lmer

I am looking at a 2x2 crossover study with period-specific baseline measurements and the according post-treatment outcome values Intervention (A or B) Sequence (AB or BA) Period (visit day1 and visit ...
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LMER model with uneven time points

Does it matter that my time series are taken at random points? All the examples I've seen have nice time series, like every day or whatever. I have what is otherwise a pretty simple model: one fixed ...
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Distribution of a quadratic form [on hold]

Problem: Let $ x \sim N_{k}(\mu, \sigma^2 I)$. Show that $x^\prime x/\sigma ^2 \sim \chi^2(k, \mu ^\prime \mu/2\sigma ^2)$ I am trying to use the following theorem result but I am kinda confused how ...
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Baseline adjustment in mixed models with two assessments

I want to exmine whether three interventions have different effects over time on an outcome that has been measured only two times (two assessments before and after treatment: baseline and follow-up) ...
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Mixed models basic

I am learning mixed models and while reading different materials I still have a couple of questions that I could not find answers. If I have 2 or more fixed effects and if the interaction is not ...
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“Nested” time-series comparison?

I'm Stick with a methodological problem and I'm not sure how to manage a possible solution. I want to compare two sets of observations made in two independent groups (15 subjects per group) over time. ...
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phylogenetic multilevel model in MCMCglmm

I'm trying to run a mixed phylogenetic model using the MCMCglmm function in the R package of the same name. In this model, I want to estimate slopes and intercepts ...
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1answer
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Random effects in GLMM [closed]

I am running at the moment a GLMM with insect abundance (count data) as response variable and 3 landscape variables and temperature as (continous) explanatory variables. So, my GLMM looks like this: ...
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Interpreting VarCorr estimates versus cor(ranef()) in lme4 mixed models

I am following-up this and this thread because I found it very difficult to understand the implications of using each of the two types of random-effect correlations. In particular, I fitted model like ...
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How to measure carryover effect in a crossover design 3x3?

I'm trying to analyse a potential carryover effect from a study with a crossover design 3x3, three treatments and three periods. My data has a latin square design with the treatment sequences CBA, ...
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How to analyze data with unequal length of observations and many zeros?

I want to analyze the impact of the rain on smoking probability. I observed people in two cities on the streets and marked the following parameters: city, gender of the person, duration of observing ...
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Generalised Logistic Regression with mixed effects - Binomial model creation / selection

I have a dataset with 72 individuals from 5 separate groups, with repeated measures - each individual was sampled 4 times. All data is binomial, and in most cases there are more 0s than 1s. I have a ...
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can I reshape my data to long format to run this model? [closed]

Let's say I want to test whether age predicts performance in a math and biology tests. Let's ...
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Interpretation of related lower-order interaction when higher-order interaction is significant

How do you investigate lower-order interactions which include one factor that is part of a significant higher-order interaction? Let's assume a research design with 4 factors (A, B, C, D), each with ...
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Should modeled means in glmm be averaged on link or response scale?

I'm using emmeans to estimate means of 4 treatment levels. The response is a count with poisson distribution. The design is randomized complete block with 14 blocks, each with single replicate of all ...
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How to analyze experiment (based on DoE and via mixed model)?

I am about to deploy my DoE which is based on six parameters with two whole plots: Temperature and relative humidity. The experiment aims at studying a sensor due to the presence of several gases (...
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plot data after lme model accounts for covariates in fixed and random effects [closed]

I have a question regarding how I can grab residuals from a linear mixed effect model (e.g., using lme from nlme in R) in order to plot data after the lme model has removed specific variables of no ...
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Model design with repeated equivalent measurements

I have a population of n individuals. For each of them, I have measured an outcome once: $Outcome_{ i} \,\,\,\ i=1..n $ I have also some measurements: for each ...
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Specifying mixed model in lmer for a single group reversal design

I have data on a simple experiment performed by one of my students looking at the effect of a single bout of aerobic exercise on working memory. The data are structured as follows: ...
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1answer
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Pairwise comparisons via emmeans

I have a question about emmeans and mixed effect model. I fit a complex model using lmer() with the following variables: A: a binary categorical predictor, between-subject B: a binary categorical ...
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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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Need help: nested fixed effects in nlme()

I have two fixed effects in a nonlinear mixed effect model. One is nested in the other, as the case here: "Specie" is nested in 'category'. ...
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How to use mixed ANOVA with 2 between-subjects and 1 within-subjects design

I know mixed ANOVA should be used when testing a data set containing within-between subjects design. As my data structure shows below, my between-subjects factor is ...
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Understanding how to weight variables

I am trying to model the "recruitment" of a deer population where recruitment is a factor of "females counted in fall" and "fawns counted in fall". e.g femaleFall:fawnsFall = Recruitment. In some ...
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Between Group comparison for parameters measured on different time points

I have a dataset of 100 patients for whom data was recorded of 3 different parameters say Heart rate, temperature and ETCO2 levels which are measured in 3 phases eg. Phase 0, Phase 1 and Phase 2. The ...
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Bootstrapping with more than one random effect

Consider an experiment with $m$ subjects and $n$ words. Every subject rates every word, producing an $(m \times n)$ data matrix $\hat{X}$. I am interested in forming a confidence interval around $f(\...
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1answer
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How to incorporate splines of random effects in lme4?

Are splines of random effects allowed in nlme but not in lme4? How to incorporate splines of random effects in lme4? ...
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Failing to understand and model market mix modelling

Hello I am have been trying to get my head around marketing mix modeling for last couple of months and have not been able to exactly figure out the nuances of the modelling. I have three years of ...
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19 views

Shall I use type III Anova() in “car” package or anova() to compare models?

In one analysis, I want to use the mixed-effects model to test the fixed effect of Condition. To find out the effect, I've seen some people use anova() to compare the model to a baseline model without ...
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2answers
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Mean Comparison test for 3 related samples

I have ratio scale data for 3 related samples. What is the statistical test that I can use to check whether there's any significant difference between the 3 groups? (I tried Friedman, but I'm doubtful ...
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1answer
55 views

How to deal with treatment effect at state level but observations at school level?

I have a panel of schools and I want to estimate the effect of a state level policy on school level outcomes (all schools in a treated state are treated). I can't use a fixed effects model since the ...
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1answer
36 views

Statistical significance testing when distributions are paired, but samples are not

I have a situation like the following: 5 distributions A, B, C, D, E of unknown type from which I can take samples to estimate the mean. I apply an intervention or treatment to all of the ...
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25 views

Mixed-effects model for categorical within- and continuous between-subjects variables

I'm using a model to simulate how tree growth rates vary with different traits, but I'm not sure how to correctly account for the non-independence in the data in my statistical tests. I generated ...
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Explanatory variable on group level in mixed model

I'm looking at how the scoring procedure influences individual behaviour in competitions. The independent variable (scoring procedure) is measured on the competition level, while the dependent ...
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Is there a distinction between the “squared semi-partial correlation” and the “semi-partial R squared” of a fixed predictor?

The package 'r2glmm' in R calculated the "semi-partial R squared" of each fixed predictor in a mixed effects model. The package describes this as "The semi-partial R squared statistic corresponds ...
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Paired experiment with trinomial response - Analysis help!

I'm looking to analyze data (in SAS) from a trial investigating the effect of a particular protective padding on preventing skin irritation at multiple body locations among spinal surgery patients. (...
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23 views

Relationship between people's insight and behavior

My main interest is to see how well people can identify the reasons behind their decisions. To measure this, I have collected 2 types of data: one set of variables that measures how important people ...
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1answer
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How to compare fixed effects of linear mixed models

I have two linear mixed models that I ran with the lmer function from the lme4 package. The models are identical except that I ...
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1answer
18 views

finding the within-person SD from a null model lme output

I just wanted to make sure I'm interpreting my lme() output correctly. I've set up a null model because I was told I could find the within-persons SD this way (...
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How to test for significant differences between growth curves in repeated measures mixed-models?

I am comparing growth of fish in different habitats and since length and age data is derived from repeated measurements (back-calculations) I am using a mixed model (R, nlme). I have data from ~50 ...
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Determining Link for GLM

I am having a great deal of difficulty understanding how to use the Generalized linear model for my data set. The response variable of interest is hatch success of sea turtles, which is a %. The ...
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How to obtain different values of “parameter k” in a mixed-effects negative binomial model?

I have a dataset with two level factors - fertilizers ("Nitrogen" or "Phosphorous") that differed in their concentration level("...
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Interaction analysis when different groups are used for the between-subjects variable and the within-subjects variable?

I would be very grateful if someone could help me out here. I have three groups: I ask one group "Should you help A?", I ask the other group "Should you help B?" and I ask the third group both ...
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Finding stability in a time series of success/failure data — Mixed Model Random Effects

I have a very large data set of success/failure data for hundreds of subjects. The chance of success is rather small but does/should stabilize over time. Subjects have varying levels of observations/...
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How to study split-plot design

Is it possible to study a split-plot design with a mixed model? I've seen a related question so I guess it is doable in general. Is there any certain function or procedure I can use? Or can you give ...
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1answer
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Multilevel Non-parametric Model: using signed ranks in a classic linear mixed model?

I have data that with my best efforts cannot be transformed into something resembling a normal distribution. Or more specifically, the residuals of the linear model I want to run on the data is in no ...
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1answer
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Does anyone know how to conduct power analysis and estimate sample size for a mixed model cross-level interaction?

I am planning for a rather simple mixed design study. I have one within-subject factor (2-level, repeatedly measure/treatment twice) and one continuous between-subject factor. Now I am interested in ...
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1answer
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What test to look at impact over time?

I am looking at the impact of a fungus on a plant over time by measuring key plant parameters (height, number of flowers, seeds, leaves etc) three times over the growing season. I have 12 replicates ...
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Can I use partial eta and/or partial omega squared for effect size estimation of each independent variable in linear mixed model regression?

I need to estimate effect size estimation of each independent variable in linear mixed model regression. Here is a code: ...