Repeated measures data occurs when more than one measurement is collected on the same unit (e.g. subject). This data cannot be analysed through normal methods because the rows in the data are not independent due to the multiple measurements. The time sequencing of the measures may not be important.
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2answers
5k 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?
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4answers
1k 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 ...
13
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2answers
4k 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 ...
12
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2answers
269 views
What to do when some time points have heavily skewed responses and some do not in a repeated measures study?
Typically, when one encounters continuous but skewed outcome measures in a longitudinal design (say, with one between-subjects effect) the common approach is to transform the outcome to normality. If ...
12
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1answer
377 views
Is there an R package for continuous time longitudinal binary responses?
The bild package appears to be an excellent package for serial binary responses. But it is for discrete time. I would like to specify a smooth function of time ...
11
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5answers
4k views
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 ...
11
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8answers
3k 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
8k views
How to determine the sample size needed for repeated measurement ANOVA?
I need some help about repeated measurement ANOVA.
We are investigating the effect of some intervention on reducing blood stream infection (BSI) rate in some wards. We plan to capture the BSI rate ...
11
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2answers
250 views
Without multi-level modeling, how to handle within-study replication in a meta-analysis, where the study is the unit of replication?
Description of the study:
I have observed a common error among meta-analyses, with regard to handling of within-study replication. It is not clear to me if the error invalidates the studies when ...
10
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4answers
2k 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 ...
10
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1answer
601 views
How is an ANOVA calculated for a repeated measures design?
The title says it all, and I'm confused. The following runs a repeated measures aov() in R, and runs what I thought was an equivalent lm() call, but they return different error residuals (although the ...
10
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2answers
1k views
What would a confidence interval around a predicted value from a mixed effects model mean?
I was looking at this page and noticed the methods for confidence intervals for lme and lmer in R. For those who don't know R, those are functions for generating mixed effects or multi-level models. ...
9
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2answers
3k views
Split-Plot ANOVA: model comparison tests in R
How can I test effects in a Split-Plot ANOVA using suitable model comparisons for use with the X and M arguments of ...
9
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2answers
4k views
Multiple comparisons on a mixed effects model
I am trying to analyse some data using a mixed effect model. The data I collected represents the weight of some young animals of different genotype over time.
I am using the approach proposed here:
...
9
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1answer
4k 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 ...
9
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2answers
3k 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 ...
9
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1answer
259 views
Predictive Modeling - Should we care about mixed modeling?
For predictive modeling, do we need to concern ourselves with statistical concepts such as random effects and non independence of observations (repeated measures)? For example....
I have data from 5 ...
9
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2answers
309 views
Longitudinal comparison of two distributions
I have the test results of a blood test administered to 2500 people four times at six-month intervals. The results primarily consist of two measures of immune response - one in the presence of ...
9
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2answers
192 views
What model for a challenging data set? (hundreds of time series with a lot of nesting)
I have quite a complicated data set to analyze, and I cant find a good solution for it.
Here is the thing:
1. the raw data is essentially insect song recordings. Each song is made of several ...
8
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3answers
498 views
How to test whether a covariance matrix has changed over two time points?
My task is to test if there's change in covariance matrix of 6 variables. Values of 6 variables are measured twice from same subjects (3 years between measurements).
How can I do that? I've been ...
8
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1answer
206 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 ...
8
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1answer
983 views
How should I analyze repeated-measures individual differences experiments?
I do quasi-experimental individual differences psychology research. I examine how people who differ in a cognitive ability (that I measure) perform on another task that always at least involves ...
8
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1answer
262 views
Can slopes in linear regressions be used as the independent or dependent variables in other regression models?
I have 100 patients and each patient have 10 longitudinal serum creatinine measurements. The estimated glomerular filtration rates (eGFR) were calculated from a MDRD formula comprising gender, age and ...
8
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1answer
657 views
Sample size for proportions in repeated measures
I'm trying to help a scientist design a study for the occurrence of salmonella microbes. He would like to compare an experimental antimicrobial formulation against a chlorine (bleach) at poultry ...
7
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1answer
764 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 ...
7
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2answers
4k 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 ...
7
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2answers
6k views
Repeated measures ANOVA with lme in R for two within-subject factors
I'm trying to use lme from the nlme package to replicate results from aov for repeated ...
7
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3answers
3k views
What is the difference between using aov() and lme() in analyzing a longitudinal dataset?
Can anyone tell me the difference between using aov() and lme() for analyzing longitudinal data and how to interpret results ...
7
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1answer
681 views
Nested/SplitModel - RepeatedMeasures/MixedModel ANOVA: levels of nesting & scripting in R
My data set has the following variables:
Treatment (4 types- fixed)
Location (8 locations- fixed)
Position in Location (3 positions per location- fixed)
Samples are taken in each position (3 ...
7
votes
2answers
2k views
How to specify specific contrasts for repeated measures ANOVA using car?
I am trying to run a repeated measures Anova in R followed by some specific
contrasts on that dataset. I think the correct approach would be to use
Anova() from the ...
7
votes
2answers
795 views
Longitudinal data: time series, repeated measures, or something else?
In plain English:
I have a multiple regression or ANOVA model but the response variable for each individual is a curvilinear function of time. How can I tell which of the right-hand-side variables ...
7
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1answer
223 views
What article or book clearly states that one can't use protected t-tests in within subjects ANOVA?
I have been asked to use protected paired samples t-tests in an analysis. The requester states that if I do not use the overall MSe from my (1 factor with four levels) within-subjects ANOVA when ...
7
votes
2answers
747 views
Correcting for multiple comparisons in a within subjects / repeated measures ANOVA; excessively conservative?
It strikes me that the available corrections for multiple comparisons in the context of a repeated measures ANOVA are excessively conservative. Is this actually the case? If so, what are some ...
7
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2answers
175 views
Estimating variability over time
I have a dataset that contains ~7,500 blood tests from ~2,500 individuals. I'm trying to find out if variability in the blood tests increases or decreases with the time between two tests. For ...
7
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0answers
679 views
How to analyse repeated measure ANOVA with three or more conditions presented in randomised order?
Context:
My question concerns a typical design in my area – a researcher takes a group of subjects (say 10) and then applies three different conditions to them to measure the change in a response ...
6
votes
4answers
852 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 ...
6
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1answer
559 views
6
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3answers
508 views
Repeated measures structural equation modeling
I need to analyse a dataset of clinical rehabilitation data. I am interested in hypothesis-driven relationships between quantified "input" (amount of therapy) and changes in health status. Although ...
6
votes
1answer
5k 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)
...
6
votes
1answer
94 views
To aggregate and lose resolution OR not to aggregate and suffer with correlated binary data?
I have data from an experiment in which each participant provides a binary response to each presented stimulus, which is either correct (1) or incorrect (0).
There are 4 different stimulus types, ...
6
votes
1answer
404 views
How to specify Bayesian mixed effects model in BUGS
I posted this earlier in the week then retracted the question when I found a good source, not wanting to waste people's time. I haven't made much progress I'm afraid. In trying to be a good citizen ...
6
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1answer
77 views
Is there a classification of physical measurements according to their statistical distribution?
I am looking for a document or research articles classifying physical or chemical measurements (or perhaps better means of measurement) according to the reference statistical distribution and ...
6
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1answer
2k views
Determination of effect size for a repeated measures ANOVA power analysis
This is a follow-up to the repeated measures sample size question.
I am planning a repeated measures experiment. We record energy usage for 12 months, then give (a randomly assigned) half of the ...
6
votes
0answers
594 views
How to use G Power 3 to calculate statistical power in mixed design ANOVA with unequal group sample sizes
In G power 3, ANOVA repeated measures within-between interaction: Only the total sample size is reported assuming equal sample size for the two groups.
My questions are:
How would it work if the ...
5
votes
2answers
169 views
Plotting and presenting longitudinal data, options?
Hypothetical Scenario: A few continuous variables, each measured repeatedly at, say 12 time points, each with say, 150 observations. There are small fluctuations from one time point to another (i.e. ...
5
votes
3answers
115 views
Matched binomial pairs
I am trying to analyse the following table:
5 5 5 5 4 5 5 5 5
3 4 3 3 4 4 3 5 5
Each number is a success score out of 5 attempts, so we can assume binomial (p, 5), for unknown p. ...
5
votes
2answers
2k 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 ...
5
votes
3answers
5k views
What is a minimum sample size for a paired t-test and what is a non-parametric equivalent if data is non-normal?
I have 4 sample pairs, let's say (x1, y1),...,(x4, y4).
What is the minimum sample size for a paired t-test?
Which assumption should I check for paired t-test?
If my data is non-normal, what is an ...
5
votes
3answers
612 views
Might be an unbalanced within subjects repeated measures?
I ran a within subjects repeated measures experiment, where the independent variable had 3 levels. The dependent variable is a measure of correctness and is recorded as either correct / incorrect. ...
5
votes
2answers
956 views
What descriptive statistics should be reported in tables and graphs when using Friedman's nonparametric test?
I'm using Friedman's nonparametric tests for repeated measures for my thesis (I tried transformations on all variables first but data was still highly skewed) and had 2 questions:
What are the best ...
