Questions tagged [anova]

ANOVA stands for ANalysis Of VAriance, a statistical model and set of procedures for comparing multiple group means. The independent variables in an ANOVA model are categorical, but an ANOVA table can be used to test continuous variables as well.

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How the Error() term in aov() decides what goes in which stratum?

I am trying to understand how the principles of nested anova in R, but I am having extreme difficulty with the error term. Imagining the simplest case. I measured plant growth in two places, A and B. ...
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Does Greenhouse-Geisser correction influence the effect size estimation, the statistical significance treshold, or both of them?

I discussed recently with one of my colleagues about the Greenhouse-Geisser correction for non-sphericity. I told him first that this correction is very conservative and that it would be more ...
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Comparing two F-test statistics

I have two groups A and B, each of which consists of 5 samples. Each sample is described in a vector of length (>1000) of continuous numeric values (characteristics). I want to test if the sample in ...
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Will Tukey multiple comparison be the same for different types of Sum Of Squares of ANOVA for an unbalanced design

I am working on Two-Way ANOVA for an unbalanced design. Will Tukey multiple comparison be the same for different types (I, II & III) of Sum Of Squares of ANOVA for an unbalanced design. I am ...
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Is ANOVA always more powerful than a two-sample t-test when the data can be blocked?

I am trying to compare the efficacy of two devices. Three different operators tested each device for a parameter of interest (the same 3 operators for each device) and yielded two data sets for each ...
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Missing cells with Type III SS

I have a linear model of the form y ~ x + z + x:z. I have unbalanced data and further have a few missing cells (data would be unbalanced even without those missing cells). My understanding of the ...
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How does R's aov function 'work better' with orthogonal contrasts?

The help page for R's aov function states: The default ‘contrasts’ in R are not orthogonal contrasts, and aov and its helper functions will work better with such ...
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What is the logic behind ANOVA on ranks?

I've read a few sources that describe ANOVA on ranks, and I am still confused on how the calculation is done, and why. Specifically: Is ANOVA on ranks just applying a rank transformation to the data ...
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Orthogonality in ANOVA and Regression Analysis

I read the following (Wikipedia) regarding contrast coding of categorical variables: Unlike when used in ANOVA, where it is at the researcher’s discretion whether they choose coefficient values ...
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AIC or ANOVA to compare models?

What are the relative merits of each approach, and which circumstances call for one rather than the other? To some extent I have a specific example in mind, which I've discussed here. In that example ...
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creating contrast matrix (limma) for two factorial in R

I am attempting to construct a contrast matrix that I can run in R, using the limma bioconductor package, but I am not sure that I have coded the contrast matrix correctly. A previous post and the ...
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When to use a chi-squared test?

This is a very basic question however I do not have a statistical background and I am currently analysing some data for my dissertation. I have constructed a survey about healthy lifestyles & ...
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When using repeated-measures ANOVA in R, what does it mean to specify Error(subject) instead of Error(subject/(A*B))?

For a two-way repeated measures design, we can specify the model using aov in the following fashion: ...
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Formulating a mixed model with nested fixed and random effects

I'm analysing the results of an experiment using a mixed (fixed and random-effects) ANOVA with nested effects and I just need someone to confirm that I have the right model. The effects in the design ...
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Three versions of the independent two sample t-test (and R)

This post concerns three versions of the independent two sample t-test: Student's t-test uses a pooled standard deviation in the denominator (all equations are shamelessly copied from Wikipedia - ...
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ANOVA vs. mixed models

I'm confused between the differences between x-way/mixed ANOVA models and mixed models. Is there a difference? If so, what is the difference and why?
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Seeking authoritative references on weighted ANOVA

I would be grateful for any reference, such as a textbook or peer-reviewed journal article (of any vintage), that contains explicit formulas for conducting a weighted ANOVA with arbitrary weights. ...
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Geometric interpretation of the difference between the means (ANOVA)

First of all, a disclosure: I'm a medical doctor trying to understand statistics for research. Coming from a non-mathematical background I can do many mistakes. I've read some traditional books of ...
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Syntax differences between aov and lmer for two-way repeated measures design

I'm working with the following data frame using R. It consists of measurements obtained from 7 subjects with two independent variables (IV1 and ...
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How to handle crossed and nested terms in a crossover design

Here comes my case: I conducted an experiment with the following design: 30 participants, each with a unique id, were screened and classified according to a trait. Then, all participants were tested ...
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The anova() function in R to compare a glm() and a glmer() models

I recently tested something regarding the stats::anova function in R. Assuming modglm is a model fitted with the ...
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Computing effect size (partial eta squared) from a RM-ANOVA's F value

I want to calculate the number of participants I need in order to get a power of 0.95, when replicating an effect. The effect size of this effect is not reported in the previous study, which is why I ...
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Is there a principled ANOVA-like approach when a "subject" factor forms a symmetric 2D matrix?

I have a dataset where the dependent variable is a similarity measure between any 2 data channels, lets call it S(i,j), with a few dozen simultaneously recorded channels (so there are quite a few ...
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Dropping columns from an orthogonal design matrix?

Hello: I’m working with a three factor (ANOVA) design that I wish to use in an MCMC chain to estimate the parameters for the main effects and treatment interactions. I wish to run MCMC analyses ...
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Mixed Anova in R

I am trying to do an anova anaysis in R. The experiment done had each subject tested in Method 1 and Method 2 as well a being in one of 4 different Levels (each subject in one group). The goal is to ...
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multiple Kruskal-Wallis instead of ANOVA for non-normally distributed data

Apologies in advanced if I supply too little or vague information, since I am a complete newbie in stats and using this forum. So I did a study which evaluated psychopathic personality traits, ...
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Testing for differences between time series with many timepoints

I think the easiest way to describe my question is with plots. I've run an experiment where I recorded data from animals' brains (EEG) at 6 depths. The animals are recorded at baseline for 25 minutes,...
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1 answer
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No value or "."returned for Mauchly's Test of Sphericity in SPSS

I am learning how to do a Two-Way Repeated Measures ANOVA in SPSS but when I try to check the Mauchly's Test of Sphericity Significance value it only displays a single decimal point. It is also ...
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How to modify the f-test null hypothesis in ANOVA

Normally the null hypothesis for a f-test in ANOVA is $H_0:\mu_1=\mu_2=...=\mu_m$ for a comparison of $m$ groups. How do I alter the f-statistic so that the null hypothesis is $H_0:\mu_1=\mu_2=...=\...
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What is the ANOVA equivalent of a matched-pairs t-test? MANOVA?

I have n subjects. I perform an experiment on all the subjects and measure the outcome in two different ways. I want to evaluate the difference between these two types of measurements. I would use a ...
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Only interested in select pairwise comparisons - Do I need to run an ANOVA first?

I have data with two biological factors. The first factor has 2 levels (say, Alive vs. Dead) and the second factor has 80 levels (protein of interest). I'm only interested in whether the mean value ...
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How is two-sample ANOVA the same as two-sample t-test?

When testing the differences between the means of two groups, I'm aware that one can use the ANOVA test, and/or the ...
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Is repeated measures ANOVA right for this experimental design? Unsure

I have 2 to 5 subjects (different sea organisms) that will be exposed to several different treatments (varied doses of bacteria). Each group is done in triplicate due to the variability of the ...
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4 votes
1 answer
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Reduced degrees of freedom using transformed data in one-way ANOVA (SAS PROC MIXED)

On pg. 88 of Design and Analysis of Experiments (8th Ed.) by Montgomery, he's analyzing square root transformed data in a one-way ANOVA. He provides an ANOVA table (SS, d.f., MS, F, p) for these data, ...
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Mixed between-within subjects ANOVA

I am wondering how interpret tables. I used a mixed ANOVA for analyzing: My within-subjects factor is time (pretest, posttest, follow-up) my between-subjects factor consists of conditions (...
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Effect size for contrasts in hierarchical Bayesian "ANOVA"

Kruschke (2014) shows in his book how to compute posterior distributions of effect sizes (standardized mean difference) for the Bayesian analogues of frequentist independent-samples t-tests, and one-...
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How is the confidence interval for variance component in "lmer" function computed by the command "confint"?

Here is the R code : ...
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Central limit theorem: applicability for assumptions of different tests

Since many statistical procedures (e.g. t-test, ANOVA, Pearson’s r (for efficient estimates)) require the normal distribution of the tested variables ('normality-assumption') one may ask if (at least) ...
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1 answer
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Scientifically reasonable or not ? exclusion of very, very uncertain values from statistical analysis

I have 5 treatments A1 .. A5 and 4 independent individuals per treatment, whose parameter X is of interest to me. My objective is to compare X among treatments, and see if one or more treatment ...
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How to best approach ANOVA with multiple response variables that might be correlated and Bonferroni Correction

I need some help verifying a simple analysis. I have completed a simple two factor experiment of more or less equal sample sizes. Let's assume for the case of this question that the sample sizes are ...
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4 votes
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619 views

ANOVA on ranks?

Once in a statistics class I've seen the suggestion that one non-parametric approach for ANOVA would be to perform the ANOVA analysis on the ranks of the original data (basically as an alternative to ...
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Partitioning variance from logistic regression

Short version How can I partition the variance from the different levels in a nested mixed-effects logistic regression? Preferably using R, but even general principles would be helpful as a start. ...
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Simulation for power analysis for higher order repeated measures ANOVA

I am attempting to find a way to perform a power analysis for a higher order repeated measures ANOVA where all factors are within-subjects (i.e., there are no between-subjects factors). I have looked ...
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4 votes
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Separate ANOVAs on subsets of data

I often read that, after obtaining complex (e.g., four-way) interactions in a factorial ANOVA, researchers decide to split their data by a factor (e.g., gender) and run separate ANOVAs for these two ...
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Exponential regression: calculating p-value and F significance

I have a set of independent data and dependent data $(X,Y)$, where I would like to do an exponential regression to obtain its p-value and significant $F$ (already obtained $R^2$ and also the ...
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Do you need to stratify / match sample for ANCOVA comparisons?

I have data about body image and weight change behaviours from $N = 397$ adolescent boys that we collected in 2000. Age ranged from $13.5$ years to $18.67$ years and the mean age was $15.92~ [SD= 1....
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Statistical test to compare different treatments over time

In my experiment I have 4 treatments (the control plus the variables: A, B, C) and I am comparing the growth among them. I have 4 replicates for each treatment. Thus 16 samples in total. Every other ...
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143 views

Is Fisher overestimating the variance here?

[NB: the title of this post used to be "Please help me decipher Fisher on ANOVA". I've edited the question to make it more focused, and modified the title accordingly.] Since anything written by R. ...
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Comparing models of different types of ANOVA - multiple comparisons?

Statistical semi-novice question: Just following up this question, the fact that the three types of ANOVA exist with an unbalanced design, and that (presumably) you don't necessarily know a priori ...
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Can paired samples be treated as un-paired for 1-way ANOVA

This may be too simple a question for this forum - it is possibly a very basic statistics question as commonly found in biomedical research. But since scientists often lack good understanding of ...
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