# Linked Questions

63 votes
2 answers
67k views

### What is a difference between random effects-, fixed effects- and marginal model?

I am trying to expand my knowledge of statistics. I come from a physical sciences background with a "recipe based" approach to statistical testing, where we say is it continuous, is it normally ...
• 1,955
10 votes
2 answers
3k views

### Why is the estimated variance of a random effect not equal to the variance of its BLUP estimates? [duplicate]

I am learning mixed effect model from here. I built a simplified model and trying to extract the $\gamma$ vector from linear mixed effect model $$y=X\beta+Z\gamma+\epsilon$$ then calculate ...
• 36.6k
10 votes
2 answers
10k views

### Conditional vs. Marginal models

I have data with an outcome of 0 or 1 (binary) representing success or failure. I also have two comparison groups (Treatment vs. Control). Each subject in the study contributed 2 observations (the ...
• 755
4 votes
2 answers
4k views

### Covariance matrix for the random effect in mixed effects model

According to this post, matrix Omega and sigma are in the results of lmer when we fitting ...
• 641
3 votes
2 answers
3k views

### Random slope and intercept correlation. Not consistent in output vs manual calculation

Lets say individuals are nested within each ID and I am trying to a predict level 1 outcome Y from a level 1 predictor X with random slopes and intercepts. Using the nlme package in R, I ran the ...
• 1,174
16 votes
1 answer
17k views

### Marginal model versus random-effects model – how to choose between them? An advice for a layman

In searching for any info about marginal model and random-effects model, and how to choose between them, I have found some info but it was more-or-less mathematical abstract explanation (like for ...
15 votes
1 answer
14k views

### Interpretation of Fixed Effects from Mixed Effect Logistic Regression

I am confused by statements at a UCLA webpage about mixed effects logistic regression. They show a table of fixed effects coefficients from fitting such a model and the first paragraph belows seems to ...
• 8,470
11 votes
1 answer
11k views

### Difference between marginal and conditional models

A marginal model accounts for the correlation within each cluster. A conditional model also takes into account the correlation within each cluster. My questions are: Does a marginal model models ...
• 141
3 votes
1 answer
6k views

### Subject specific vs population average predictions

I am in doubt whether in my thesis I should report on the subject specific predictions of the probability to respond with an 'I don't know' answer, or the population average. Consider for example the ...
• 790
1 vote
0 answers
483 views

### 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 ...