Questions tagged [repeated-measures]

Repeated measures data occur when more than one measurement is collected on the same unit (e.g. subject). Use this tag for RM-ANOVA together with [anova] tag.

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24
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2answers
20k views

Why do lme and aov return different results for repeated measures ANOVA in R?

I am trying to move from using the ez package to lme for repeated measures ANOVA (as I hope I will be able to use custom ...
13
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1answer
3k views

Determining true mean from noisy observations

I have a large set of data points of the form (mean, stdev). I wish to reduce this to a single (better) mean, and a (hopefully) smaller standard deviation. Clearly I could simply compute $\frac{\sum ...
26
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3answers
57k views

Post hoc test after ANOVA with repeated measures using R

I have performed a repeated measures ANOVA in R, as follows: aov_velocity = aov(Velocity ~ Material + Error(Subject/(Material)), data=scrd) summary(aov_velocity) ...
27
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3answers
44k views

Differences between MANOVA and Repeated Measures ANOVA?

What is the difference between a repeated measures ANOVA over some factor (say experimental condition) and a MANOVA? In particular one website I stumbled across suggested that MANOVA does not make the ...
105
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2answers
191k views

What is covariance in plain language?

What is covariance in plain language and how is it linked to the terms dependence, correlation and variance-covariance structure with respect to repeated-measures designs?
43
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8answers
41k views

Is it valid to include a baseline measure as control variable when testing the effect of an independent variable on change scores?

I am attempting to run an OLS regression: DV: Change in weight over a year (initial weight - end weight) IV: Whether or not you exercise. However, it seems reasonable that heavier people will lose ...
11
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2answers
5k 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: ...
4
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1answer
2k views

What experimental design is this?

I collect blood from one human (donor), separate leukocytes and put $2\times10^6$ of them per each well of five: well 1: $2\times10^6$ Lk (leukocytes) well 2: $2\times10^6$ Lk well 3: $2\times10^...
20
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5answers
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Post-hocs for within subjects tests?

What is the preferred method for for conducting post-hocs for within subjects tests? I've seen published work where Tukey's HSD is employed but a review of Keppel and Maxwell & Delaney suggests ...
24
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2answers
4k views

Does it make sense for a fixed effect to be nested within a random one, or how to code repeated measures in R (aov and lmer)?

I have been looking through this overview of lm/lmer R formulas by @conjugateprior and got confused by the following entry: Now assume A is random, but B is fixed and B is nested within A. ...
20
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2answers
33k views

Repeated measures ANOVA with lme/lmer in R for two within-subject factors

I'm trying to use lme from the nlme package to replicate results from aov for repeated ...
16
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3answers
16k views

A non-parametric repeated-measures multi-way Anova in R?

The following question is one of those holy grails for me for some time now, I hope someone might be able to offer a good advice. I wish to perform a non-parametric repeated measures multiway anova ...
8
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2answers
4k views

How can I test for differences in variation between groups in a mixed model (lme4)?

I would like to test for differences in variation, not in means, between two sites. By looking at a boxplot of my data I see that bird song in one site look much more variable in length than in ...
22
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2answers
14k views

Paired t-test as a special case of linear mixed-effect modeling

We know that a paired t-test is just a special case of one-way repeated-measures (or within-subject) ANOVA as well as linear mixed-effect model, which can be demonstrated with lme() function the nlme ...
11
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1answer
5k views

How to perform a 4 by 4 mixed ANOVA with between- and within-subjects contrasts using R?

Beginner user of R here struggling with a repeated measures ANOVA. I have a dataset that consists of one between subjects factor with 4 levels (coded in a single variable called 'groups'), and one ...
8
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2answers
2k views

Repeated measures ANOVA vs. factorial ANOVA with subject factor: understanding “error strata” and Error() term in aov

Consider repeated measures ANOVA (RM-ANOVA) with one within-subject factor A and several measurements per subject for each level of ...
48
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2answers
86k views

Using lmer for repeated-measures linear mixed-effect model

EDIT 2: I originally thought I needed to run a two-factor ANOVA with repeated measures on one factor, but I now think a linear mixed-effect model will work better for my data. I think I nearly know ...
27
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5answers
21k views

Example reports for mixed-model analysis using lmer in biology, psychology and medicine?

As the general consensus seems to be to use mixed-models via lmer() in R instead of classical ANOVA (for the often cited reasons, like unbalanced designs, crossed ...
32
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5answers
9k views

Modelling longitudinal data where the effect of time varies in functional form between individuals

Context: Imagine you had a longitudinal study which measured a dependent variable (DV) once a week for 20 weeks on 200 participants. Although I'm interested in general, typical DVs that I'm thinking ...
9
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1answer
3k views

Equivalence between a repeated measures anova model and a mixed model: lmer vs lme, and compound symmetry

I have some trouble obtaining equivalent results between an aov between-within repeated measures model and an lmer mixed model. ...
14
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1answer
844 views

Equivalence of (0 + factor|group) and (1|group) + (1|group:factor) random effect specifications in case of compound symmetry

Douglas Bates states that the following models are equivalent "if the variance-covariance matrix for the vector-valued random effects has a special form, called compound symmetry" (slide 91 in this ...
9
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2answers
10k views

Is a “split plot” ANOVA with two factors the same as two-way ANOVA with repeated measures in one factor?

Is a "split plot" ANOVA with two factors identical to two-way ANOVA with repeated measures in one factor? if not, what is the distinction?
10
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1answer
7k views

How to write the error term in repeated measures ANOVA in R: Error(subject) vs Error(subject/time)

My question is very closely related to a previous post Specifying the Error() term in repeated measures ANOVA in R. However, I would like to get more insight into how to define the error term. ...
5
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1answer
618 views

Difference between Repeated measures ANOVA, ANCOVA and Linear mixed effects model

What is the best way to analyze these data: Subjects are divided in two "Group" (Treatment A and B). "Weight" is recorded before and 3 months after treatment. Outcome variable: ...
35
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1answer
37k views

Multiple comparisons on a mixed effects model

I am trying to analyse some data using a mixed effect model. The data I collected represent the weight of some young animals of different genotype over time. I am using the approach proposed here: ...
17
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1answer
16k views

Unbalanced mixed effect ANOVA for repeated measures

I have data from patients treated with 2 different kinds of treatments during surgery. I need to analyze its effect on heart rate. The heart rate measurement is taken every 15 minutes. Given that ...
13
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1answer
35k views

Linear regression with repeated measures in R

I was unable to figure out how to perform linear regression in R in for a repeated measure design. In a previous question (still unanswered) it was suggested to me to not use ...
16
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2answers
17k views

Which multiple comparison method to use for a lmer model: lsmeans or glht?

I'm analyzing a data set using a mixed effects model with one fixed effect (condition) and two random effects (participant due to the within subject design and pair). The model was generated with the <...
10
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2answers
21k views

How to correctly treat multiple data points per each subject

I am currently arguing with someoe on how to correctly treat data with multiple measurements for each subject. In this case data was gathered for each subject within a short time for different ...
10
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2answers
13k views

Are degrees of freedom in lmerTest::anova correct? They are very different from RM-ANOVA

I am analyzing the results of a reaction time experiment in R. I ran a repeated measures ANOVA (1 within-subject factor with 2 levels and 1 between-subject factor with 2 levels). I ran a similar ...
11
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1answer
1k views

Repeated measures analysis: why nest experimental factors within subject factor?

Consider a pure repeated measures design, with (let's say) 3 experimental within-subject factors A, B, and C, and (for simplicity) 2 levels per factor. So we have 2*2*2 = 8 measurements per subject. ...
10
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1answer
5k views
9
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4answers
1k views

Develop a statistical test to distinguish two products

I have a data set from a customer survey, I want to deploy a statistical test to see whether there is significance difference between product 1 and product 2. Here is a data set of customers' reviews....
1
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1answer
2k views

Accounting for time in repeated measures glmm, R

I have some count data of advanced stage juvenile snails in tanks that are sampled every 4 days for 4 sample points. I want to see how much the snail development stages change with a changing dosage ...
9
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2answers
20k views

Understanding repeated measure ANOVA assumptions for correct interpretation of SPSS output

I am investigating whether different reward conditions may affect task performance. I have data from a small study with two groups, each with n=20. I collected data on a task that involved performance ...
6
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1answer
3k views

Is using error bars for means in a within-subjects study wrong?

I seem to recall one of my professors saying that error bars are completely uninformative when comparing repeated measures taken from a single group. Is that true? Surely many studies compute the ...
6
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1answer
9k views

Friedman's test and post-hoc analysis

I am carrying out a statistical analysis for my research. I am using a Friedman's test with post hoc analysis. At present I am using the function ...
4
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2answers
4k views

Why is Pillai's trace equal to partial eta squared in a repeated measures MANOVA (profile analysis)?

I conducted a repeated measures MANOVA using the GLM command in SPSS, with one between-subjects IV (two levels) and 10 DVs (repeated measures). According to Tabachnick and Fidell (Book: Using ...
3
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1answer
2k views

Equal standard errors for all levels of a categorical factor in lmer

I have a question about the standard error of mixed model parameters estimated using the lmerTest package. I have 12 sites with 6 treatments over each site. I ...
5
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2answers
940 views

Random intercepts model - one measurement per subject

I have repeated measurements on several hundred subjects. I plan to fit a random intercepts model. Most subjects have 3 to 4 measurements but about 20% only have one measurement. For the subjects ...
6
votes
1answer
244 views

Which stats tests to use? Bee flight activity quantified during an eclipse

I'm trying to perform a statistical analysis but not sure what test is most appropriate. The experiment and snippet of sample data are below: Methods: Bee flights from a beehive were recorded, ...
4
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5answers
6k views

Comparing the within-subject variance between two groups of subjects

If each subject has repeated a test multiple times, I am able to compute the mean and variance of their performance. (I am assuming the results to be normally distributed). 1) If it is the variance ...
20
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3answers
30k views

When is a repeated measures ANOVA preferred over a mixed-effects model?

In response to this question, regarding whether my design where I randomly presented participants with pictures from different categories was an example where I should use a repeated measures ANOVA, I ...
15
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2answers
8k views

Can I do a PCA on repeated measures for data reduction?

I have 3 trials each on 87 animals in each of 2 contexts (some missing data; no missing data = 64 animals). Within a context, I have many specific measures (time to enter, number of times returning ...
10
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2answers
9k views

Precisely how does R's coxph() handle repeated measures?

Context I'm attempting to understand how R's coxph() accepts and handles repeated entries for subjects (or patient/customer if you prefer). Some call this Long format, others call it 'repeated ...
12
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1answer
3k views

Compute partial $\eta^2$ for all fixed effects anovas from a lme4 model

Disclamer: I wasn't sure where to post this question: CV or SO, but eventually decided to try here first I've been asked by one of the reviewers to add effects sizes (preferably $\eta^2_p$ which is ...
10
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1answer
10k 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 ...
7
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1answer
1k views

Difference between (factor|group) and (1|factor:group) specifications in lme4

I have a repeated measures from clusters, over several years, and I expect the cluster effect to vary each year. Year is coded as a factor, with '1' as reference level. I have tried the following: <...
8
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3answers
15k views

Non-parametric test equivalent to mixed ANOVA?

I have an experiment with two groups under different conditions where a single dependent variable is measured repeatedly at multiple times. It seems the right parametric test to use here is two-...
6
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4answers
2k views

If a statistics doesn't reveal a significance do I have to calculate power for it?

Following the design and data described in this question, I did a simple one-way within-subjects repeated-measures (RM) ANOVA and found some significant p-values. I then applied non-orthogonal post-...

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