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 to compute confidence interval in ANOVA with repeated measures?

I made a model using repeated measures univariate ANOVA in R. ...
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Are there realistic/relevant use-cases for one way ANOVA?

I have trouble imagining realistic research questions that can be answered by a one way ANOVA. Two or more ways with interaction terms and perhaps mixed factors (within and between subjects), sure you ...
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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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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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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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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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238 views

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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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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381 views

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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827 views

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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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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445 views

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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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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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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856 views

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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616 views

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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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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1answer
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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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445 views

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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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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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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890 views

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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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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239 views

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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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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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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Appropriate use of difference adjusted CIs in error bars for mixed ANOVA's time * group interaction

I have performed a mixed design ANOVA with time (pre-post) and group (treatment vs control) as variables. I'm wondering if it's sensible to use between subjects difference adjusted CIs (from Baguley, ...
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1answer
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Compare three groups with very small sample size

I have three treatments: control, treatment1, and treatment2. A total of four patients were examined after receiving each of these three treatments. The dependent variable is continuous. My dataset ...
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Three-Way Anova: What does a significant three way interaction tell you conceptually?

Here's a made up example. Let's say that I have two factors, energy drink (Gatorade vs water) and gender (male and female). The outcome variable is mile time. A significant two way interaction between ...
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1answer
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GLM on non-integer data

I'm looking for a recommendation on what GLM I could do with non-integer data. Brief background of what I am doing: I'm wanting to combine calculated herbivory rates with abundance data, to compare ...
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ANOVA/ANCOVA - how to analyse

In a basic research design where you want to test how some intervention (let's say our IV is 'drinking' with the categories water; sprite; and rum) affects some continuous measurement (let's say ...
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1answer
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How do I analyse datasets with large and small values, three explanatory variables, and is not normally distributed?

I have been trying to figure out the best way to analyse my data for some time and I am just working myself into a pit of confusion. Briefly, I have taken a whole bunch of physiological measurements ...
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1answer
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Interaction is not significant in ANOVA, but significant in Regression, which is nonsense

Variables that I have: randomization (categorical): control / low / high sesdummy (categorical): low / high fairness (continuous) I wanted to see if there was an interaction effect between two ...
3
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1answer
292 views

R: Power analysis for a 2 by 2 within-within ANOVA interaction effect [pwr::pwr.f2.test()]

Background I would like to perform a power analysis for the interaction effect in a 2 by 2 within-within ANOVA design. I would like to crosscheck that I am performing this correctly using the ...
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ANOVA-like equivalence testing to measure invariance

EDITED TO ADD CONTEXT: I've a set of measurements arranged in a matrix $A \in R^{n \times m}$, where $A_{i,j}$ is the value of a function for sample $i$ under transformation $t$, that is $A_{i,j} = f(...
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239 views

Multiple comparisons between two groups (non-parametric)

Update Added more details about the Experimental setup. My experiment comprised two groups, control (N=25) and experimental (N=26). Each participant belonged to one group. Their performance has been ...
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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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195 views

What's special about orthogonal contrasts?

In my Design and Analysis class we talked about orthogonal contrasts when it comes to running an ANOVA for one factor of several levels. I understand what it means for two contrasts to be orthogonal. ...
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confusion about the link between residuals, error terms, sample size and CLT in ANOVA

I feel a little confused about the assumption of the ANOVA and what it ensures mathematically the errors have to be iid and normally distributed N(0,1). independance of observation. Is it not a ...
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Should this be a one-way repeated measures anova?

I'm a new phd researcher and I just completed my first set of experiments. Participants played the same game using three different control mechanisms. In the game they had to complete a series of ...
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Test for significant difference between two groups over time

I have two different species of chicken in my chicken farm: species A and B. I have 60 chicken of species A and 60 chicken of species B. Over a three month period I wish to investigate whether they ...
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Nonparametric alternative to a mixed-design ANOVA

I'm working on the statistical analysis of a listening test (based on the MUSHRA [1]) where I'm trying to compare the sound quality degradation introduced by the processing of 3 different algorithms. ...
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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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