Tagged Questions
3
votes
0answers
61 views
Mixed/hierarchical/multilevel model for n-of-1/single-subject design: incorporating baseline data?
So I often do little self-experiments where I blind & randomize things; these can be formulated as your normal t-tests, but sometimes the measured metrics have extensive baselines which seem like ...
0
votes
0answers
24 views
1
vote
1answer
68 views
“ random effects must be less than the number of observations” error in lmer package
I'm trying to implement a regression model with both fixed and random effects. The package I use is the lme4.
I want to find the relationship between the ...
1
vote
1answer
81 views
Lmer model design
My data is a series of repeated measures in time (14 measures). I am trying to model the variable HbA1c which is a blood test performed at each visit to measure the ...
2
votes
1answer
39 views
Quantify strength of association of two continuous variables while controlling for random effects
I have a data set from a repeated measures experimental design with different sets of stimuli. I want to know how strong the association between the continuous dependent variable and the continuous ...
0
votes
1answer
45 views
how to test for overdispersion in Poisson lmer()
I have the following model:
> model1<-lmer(aph.remain~sMFS1+sAG1+sSHDI1+sbare+season+crop
+(1|landscape),family=poisson)
...and this is the summary ...
1
vote
0answers
44 views
Mixed-effect modeling with paired observations & bounded response variables
I am quite new in the field of mixed-effect modeling. For a beginner like me, I guess I combine several levels of complication in my analysis: paired observations & bounded response variables. I ...
2
votes
1answer
129 views
3
votes
1answer
113 views
Checking for outliers in a glmer (lme4 package) with 3 random factors
I have a question relating to the checking for outliers and / or influential points in my dataset using a glmer model with 3 random variables. I'm investigating the ...
0
votes
0answers
26 views
Linear model when both dependent and independent variables have unpaired replicates
I've got a set of experiments where 3 replicate measurements are done for rat cell lines and for human cell lines under different conditions using various compounds. I am trying to predict the ...
3
votes
0answers
59 views
Linear mixed effects model structure feedback
We are investigating the effects of a treatment (versus untreated control) on insect abundance. The study consists of 5 geographically separated study site replicates. Treatments were applied to 1 ...
2
votes
1answer
94 views
Linear mixed effect models: how to construct a suitable null model
Lets take as an example a repeated measures design with 10 subjects that are all reading the same letter strings and pressing a button as soon as they determine whether the string is valid English ...
0
votes
0answers
50 views
Random intercept for different groups of subjects
Is there a way to specify two different random intercept terms for two sub-groups of subjects within a single mixed model? The reason why I'm interested is that it seems that the inter-personal ...
0
votes
0answers
150 views
Using lme4 for case-controlled logistic regression?
I would like to use lmer for a conditional (or case-controlled or matched pairs) mixed effects logistic regression. However, I am not aware of any published use of ...
0
votes
0answers
59 views
When using lmer is a random intercept being estimated more than once if specified in seperate grouping factors?
I know there are a slew of lmer specification questions already floating around. Please let me know if this is a duplicate, or if it is deemed off-topic, and I'll delete it.
I am using a forward ...
2
votes
0answers
57 views
How close to zero should the sum of the random effects be in GLMM (with lme4)
I'm using the lme4 package in R to do some logistic mixed-effects modeling.
My understanding was that sum of each random effects should be zero.
When I make toy ...
2
votes
0answers
134 views
How to construct GLMM model for repeated measures with binary responses with lmer
In my experiment I assigned subjects to one of the 3 treatments A, B or C. Within each treatment, a single subject was tested with two models sequentially. The test sequence was randomized. The ...
10
votes
0answers
181 views
In a multi-level model, what are the practical implications of estimating versus not-estimating random effect correlation parameters?
In a multi-level model, what are the practical and interpretation-related implications of estimating versus not-estimating random effect correlation parameters? The practical reason for asking this ...
3
votes
2answers
532 views
Variance-covariance matrix in lmer
I know that one of the advantages of mixed models is that they allow to specify variance-covariance matrix for the data (compound symmetry, autoregressive, unstructured, etc.) However, ...
0
votes
0answers
100 views
Details on specifying random parameters in 3-level HLM in R
I am used to fitting 3-level HLM with HLM software, but now I am moving to lme or lme4, from package nlme in R. Unfortunatelly, though, I am struggling a little bit with the proper ...
0
votes
0answers
82 views
Generalized linear mixed model in R [duplicate]
Possible Duplicate:
Generalized Linear Mixed Model in R with repeated measures
I am trying to investigate how four variables (var1=continuous, var2=factor, var3=factor, var4=continuous) ...
6
votes
2answers
547 views
Sample size calculation for mixed models
I am wondering if there are any methods for calculating sample size in mixed models? I'm using lmer in R to fit the models (I have random slopes and intercepts).
11
votes
0answers
542 views
1
vote
0answers
178 views
Analyzing split-plot design in lme4 in R
I have the data from a split-plot design where A is my whole plot fixed factor with two levels and B is my subplot fixed factor with 2 levels and C is my random block factor. How do I analyse these ...
2
votes
0answers
177 views
1
vote
1answer
454 views
Understanding signficant interaction with non-significant main effects [duplicate]
Possible Duplicate:
How to compute significant interaction estimates when main effect is not significant?
I am an applied linguist and I am modelling responses to a vocabulary test taken by ...
0
votes
0answers
123 views
multilevel-model, lmer()-spelling and interpretation?
I m working on a piecewise linear growth model and I need help to understand how to write my lmer() code and how to interpret the ...
4
votes
2answers
412 views
Contrast for hypothesis test in R (lmer)
I'm running a lmer mixed effects model with a four-level factor (levels "0","10","100","1000") as the fixed effect.
lmer(free ~ reward.f + (1|S), longdata)
I ...
3
votes
0answers
80 views
Testing for mediation using LMER and a Freedman and Schatzkin's method (in R)
I'm trying to analyse, whether the effect of answer correctness ($X$, binary) on confidence ratings ($Y$, continuous) in some psychological task is mediated by another rating ($M$, continuous). In ...
3
votes
0answers
220 views
How to interpret coefficients of a multivariate mixed model in `lme4` without overall intercept?
I'm trying to fit a multivariate (i.e., multiple response) mixed model in R. Aside from the ASReml-r and SabreR packages (which ...
5
votes
0answers
273 views
simple repeated measures syntax - lme vs. lmer
I'm trying to look for significant effects on "similarity" (of "isinpair" and controlling for time effects) using repeated measures with an in group sample. The intervention "isinpair" occurs after a ...
1
vote
2answers
960 views
REML vs ML stepAIC
I feel overwhelmed after attempting to dig into the literature on how to run my mixed model analysis following it up with using AIC to select the best model or models. I do not think my data is that ...
6
votes
1answer
1k views
Understanding the random effect in linear mixed models (lme4, R)
I am familiar with linear regression models but the random section of linear mixed models just melts my mind. I did find an excellent guide that could have helped me but the languageR package is not ...
4
votes
1answer
445 views
Completely different results from lmer() and lme()
I got completely different results from lmer() and lme()! Just look at the coefficients' std.errors. Completely different in both cases. Why is that and which model is correct?
...
3
votes
1answer
198 views
How to deal with quasi-complete separation in a logistic GLMM?
Update: Since I now know that my problem is called quasi-complete separation I updated the question to reflect this (thanks to Aaron).
I have a dataset from an experiment in which 29 human ...
15
votes
3answers
693 views
Interpreting three forms of a “mixed model”
There's a distinction that's tripping me up with mixed models, and I'm wondering if I could get some clarity on it. Let's assume you've got a mixed model of count data. There's a variable you know you ...
3
votes
2answers
364 views
Can't find p-values in the output from lmer() in the lm4 package in R
I'm a new user of mixed models and through the material I've been reading there are always probability values (p>t) or (p>z) that estimate the importance of a level of a factor in the model. However, ...
1
vote
2answers
641 views
Using glmer to replicate result from lmer for mulitlevel modelling in R
Having read from the internet that glmer and lmer are similar thing (correct me if I am wrong), just ...
6
votes
2answers
2k views
What is rank deficiency, and how to deal with it?
Fitting a logistic regression using lme4 ends with
Error in mer_finalize(ans) : Downdated X'X is not positive definite.
A likely cause of this error is ...
4
votes
2answers
732 views
Random effect equal to 0 in lmer in R
Sorry if Im missing something very obvious here but I am new to mixed effect modelling.
I am trying to model a binomial presence/absence response as a function of percentages of habitat within the ...
6
votes
1answer
564 views
2
votes
1answer
181 views
Shouldn't the beta estimates always be the same using lm and lmer?
Can anyone tell me under what conditions the beta estimates differ between lm and lmer with a random intercept? I came across a situation where the fixed effect differed considerably. I thought the ...
4
votes
1answer
862 views
Diagnostic plots for lmer
I am trying to produce a glmm using the lme4 package in R. To validate my model I would like to produce some diagnostic plots ...
6
votes
1answer
258 views
Why the introduction of a random slope effect enlarged the slope's SE?
I'm trying to analyze effect of Year on variable logInd for particular group of individuals (I have 3 groups). The simplest model:
...
7
votes
2answers
2k views
Questions about how random effects are specified in lmer
I recently measured how the meaning of a new word is acquired over repeated exposures (practice: day 1 to day 10) by measuring ERPs (EEGs) when the word was viewed in different contexts. I also ...
6
votes
1answer
361 views
Why do I get wildly different results for poly(raw=T) vs. poly()?
I want to model two different time variables, some of which are heavily collinear in my data (age + cohort = period). Doing this I ran into some trouble with lmer ...
7
votes
0answers
1k views
How to estimate variance components with lmer for models with random effects and compare them with lme results
I performed an experiment where I raised different families coming from two different source populations, where each family was split up into a different treatments. After the experiment I measured ...
1
vote
0answers
199 views
Degrees of freedom/significance of group-level predictors in lmer
I am familiar with the debate surrounding Bates's decision to exclude p-values for mixed effects regression coefficients in lmer. However, I operate in a very p-value-focused discipline and am trying ...
1
vote
0answers
351 views
False convergence warning message in lmer
I will try to explain my data as good as possible.
So we taged 13 different whales with a tag that records time, depth, speed, angle of descent and ascent 25 samples every second.
The normal diving ...
2
votes
2answers
199 views
How to specify a multilevel regression using lmer function in R?
I am trying to analyse the effects of clipping (33% and 66%) and season (1, 2 and 3) on species richness. I have a control (no clipping, in no season) that the values are nested in.
I am having ...
