Analysis of Covariance. This is really a special case of multiple linear regression, used in ANOVA-like settings with some continuous covariates in addition to the categorical ones.

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Is there any test, like Mann Whitney U test or Kruskal Wallis test, that allows me to include a categorical covariate (like an ANCOVA)?

Here is my question: I want to know if there is a test that allow me to do an nonparametric ANCOVA. Let me explain: I am looking for a Mann-Whitney-U and a Kruskal-Wallis, but I want to include a ...
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7 views

anova versus LME

I have a very simple model and problem, but am confusing myself in model comparisons. Please help. I am running a model that is a single group pre-/post-test design. No control group. I am running an ...
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ancova for single group pre/post design

I have a simple question that I am looking for verification that I am right in interpretation. I have a single group design (no control) and want to look at changes in pre/post test scores. I have ...
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6 views

Decomposing a mixed ANCOVA

I am currently analyzing some data for a face perception study in which participants indicate preferences for one of two similar faces of either sex (i.e., face sex is a within-subjects variable). I'm ...
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5 views

Tukey HSD for multuple variables and single variable giving different results [duplicate]

I have tried to run Tukey HSD for multi-variable dataset. However, when I run the same test on a single variable, the results are completely opposite. To be more specific: code: ...
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Experiment with eels

I have carried out an experiment to study the physical effect of the insertion of a pit tag in the dorsal body of the eel. Thus I selected at random 49 eels and insert a small pit-tag (8.0 mm long x ...
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Selecting covariates for Ancova

I'm running ANCOVA to measure if changes made to a Web Site have been effective or not. The web pages have been clustered into different issues. Test Group : Set of URLs pertaining to an issue which ...
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8 views

Does Sample Size Affect Partial Eta Squared values when running a Mancova or Ancova?

I am currently running an ANCOVA and MANCOVA for my research and need some help in terms of understanding the Partial Eta Squared(PES) values given to me off on SPSS. I am first wondering if with PES ...
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17 views

Change from baseline cannot use ANCOVA

I have the following model: final count ~ baseline count + factor The factor has four levels and there is an interaction between baseline count and factor. This ...
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Building a model for research question

The question of interest is whether the relationship between A and B is the same for each level of Type. The data is in long format and looks somewhat like this... A is a numerical variable and so ...
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Interaction effects and ANCOVA

I conducted an ANOVA for a 2x2 design and obtained a main effect and an interactions. However, I also measured a variable that is known to impact this effect and I re-did the analysis in an ANCOVA. ...
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14 views

Is ANCOVA partial or semi-partial?

I thought I had it figured out, but I just wanted to verify: I understand that HMR is just like running a series of ANCOVAs after each level. Am I right to assume that when we run an ANCOVA or HMR, we ...
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17 views

Which statistical test is most appropriate for my count data?

I did a study looking at how the number of times a specific behaviour is performed during a courtship ritual is affected by temperature treatment, while trying to control for the body size of the male ...
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22 views

What does the p value for a covariate in a two-way ANCOVA (or factorial ANCOVA) really mean?

Given that the covariate aims to reduce the variance in the error term, what does the p-value mean for a covariate in a two-way ANCOVA? I assume the "correction" is applied no matter what the p-value ...
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18 views

Standard Deviations or Standard Errors for Adjusted Means in ANCOVA?

I think it is standard to report standard errors (SE) for adjusted means after conducting ANCOVA. However, some people claimed it is more meaningful to provide standard deviations (SD) instead of SE. ...
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24 views

ANCOVA interpretation

I have a continuous independent variable (AGE_CONT), a categorical independent variable (EXP_CATER, within subject, three ...
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1answer
16 views

What analyses do I use?

If I have two categorical IVs and one continuous IV and I want to see if the two categorical IVs predict a continuous DV over and above the effect of the continuous IV, what analysis should I use?
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48 views

Two-way ANOVA vs ANCOVA in R

Following this and other sources of information on how to perform ANOVA and ANCOVA in R, I got very confused on the difference between the two on how to compute this difference. Please consider the ...
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Quasi-experiment: sample size & statistics

I am conducting a quasi-experimental research in a school, where I have access to 100 students who are chosen as classrooms and who will be the participants of the study. I am interested in the ...
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12 views

Is it an ANCOVA?

In a study, baseline pulse is recorded. Participants are asked to watch a funny video and a thrilled video for 10 minutes. Pulse is recorded again. The objective of the study is to investigate ...
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21 views

How to plot identical slopes for an ANCOVA (1 categorical variable(2 levels) with 2 covariates) using ggplot2

I am trying to compare and plot regression lines of an ANCOVA when their slopes are the same and no interaction effect There are two sets of ANCOVAs plots that I am trying to create: a) 1 ...
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1answer
18 views

Showing that $\sum_{i=1}^{n}\sum_{j=1}^{n}(a_{i} - a_{j})^2 = 2n \sum_{i=1}^{n}(a_{i} - \bar{a})^2$

I wish to show $\sum_{i=1}^{n}\sum_{j=1}^{n}(a_{i} - a_{j})^2 = 2n \sum_{i=1}^{n}(a_{i} - \bar{a})^2$ for any numbers $a_1, a_2, ..., a_n$. I assume the first step $+\bar{a}$ and $-\bar{a}$ in the ...
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33 views

Factorial ANCOVA: Independence of the covariate and treatment effects

I would like to test whether the assumptions of a 2x3 ANCOVA are met. How do I exactly test the assumption "independence of the covariate and treatment effects" in this case? I proceeded as follows: ...
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27 views

multiple linear regression with factors

I am conducting a multiple regression analysis on a number of variables to determine the dependent variables. However, some of these variables are factors (have entries 1 or 0). If general ...
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Controlling for White Matter when looking at a sub-section of White Matter in the Brain - Valid Statistically?

I am interested in other people's opinion on the following matter. I have just come across a brain imaging paper that looks at differences in the volume a sub-section of white matter (SS) in the ...
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reconciling Linearity and Multicollinearity assumptions in ANCOVA

For ANCOVA, many textbooks and other resources require, among other assumptions, that covariates be linearly related to the dependent variable, which makes sense. However, many of the same sources ...
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23 views

Different results when conducting regression and ANCOVA in SPSS [closed]

I'm conducting a regression analysis with two binary categorical variables and one continuous variable as independent variables. From my understanding, the results should be identical as the results ...
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ANCOVA--Introduce second covariate

I am conducting a pretest-posttest ANCOVA with a control group in which I covary the pretest data and use the posttest data as the dependent (Jobs). Time is a repeated measure with 6 pretest and 9 ...
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18 views

Can I input a categorical variable (2 levels) as a covariate in an ANCOVA?

In my study I have two groups that were tested on different days. One of the groups received an additional behavioural test that the other did not and I want to ensure that this does not have a ...
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22 views

Why do needed sample sizes for ANCOVA versus OLS differ so much?

I am planning a study of the effect of an intervention on two groups. While computing the appropriate sample size (using GPower) for the study, I noticed that ANCOVA requires about 4x the sample as an ...
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14 views

ANCOVA not significant

How can it be explained that, when including covariates (thus performing an ANCOVA), there's no more main effect? Is it because there are other possible covariates that are not included in the ANCOVA, ...
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24 views

Non significant main effect after controlling for covariates [duplicate]

After doing a t-test that showed a significant difference, I did an ANCOVA with 3 covariates. The ANCOVA showed no significant effect of the variable that did show a significant difference in the ...
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36 views

Proper regression method for multiple continuous independent and a single continuous dependent variable?

I have 3 continuous (actually ordinal) independent variables and a single continuous dependent variable. I'm trying to sort out which regression method I should use in this case. MANOVA appears to ...
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51 views

How can I conduct a non-parametric version of MANCOVA in R?

Is it possible to transform my variables to their ranks and apply MANCOVA to the transformed data, just like how it is done in rank ANCOVA?
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Should I use repeated measures ANCOVA for single group study?

in my study I have only one treatment group (no control group), and I want to examine the changes of three DVs, so I have a pre, middle, and post surveys, and the presurvey was administered before the ...
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1answer
55 views

Can ANCOVA be used with a dichotomous dependent variable? If not, what have these authors done?

As stated above, if and how can ANCOVA be used with a dichotomous variable as the dependent/outcome variable? I found an article of which I wish to replicate some analyses ...
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7 views

Test that constant input corresponds to constant output

This may be a silly question... I have 2 times series: S1 and S2 The assumption is that the values of S2 are dependent on the values of S1. When I graph S1 and S2 for a period of time when S1 is ...
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28 views

Mixed Methods Analysis of Variance with a maximum likelihood approach

I am having trouble with a major analysis change suggested by a reviewer for my paper. I will start by stating what I did in the paper: I was interested in seeing subjective interest in two types of ...
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38 views

Equivalence of ANOVA and Linear Regression

There exist a number of resources explaining how a basic one-way ANOVA is equivalent to a linear regression model using effects coding. Interestingly, my statistics education has primarily focused ...
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22 views

Newbie question: can a categorical IV be included in ANCOVA with only a couple observations in 1 group

I think this is a pretty simple question, but I have been unable to find an appropriate answer. Please help. I have identified a sub-sample of my treatment group that were taking a medication that ...
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Covariate and DV - can they be the same?

I have two IVs (personality and teaching method) and a DV of self-esteem. I'm running a pretest/posttest ANCOVA (as I can't randomise) and am not sure if the DV and covariate can be the same. Can I ...
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1answer
20 views

adjust a non normally distributed numerical variable for a categorical covariate

Length of hospital stay was measured in 3 groups of patients (group 1,2,3) the length of stay is numerical continuous e.g. 4 days of 6 days one of the other variables is a confounder measured as a ...
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28 views

R: ANCOVA with two time points and one covariate

Consider the following experiment: Patients with epileptic seizures have blood samples taken when arriving at the hospital. Additional samples are being taken for a study of a new blood biomarker of ...
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52 views

R² of ANCOVA mostly driven by covariate

Based on data from a scenario-based experiment, I am running a 2x2x2 ANCOVA with one continous covariate (sample size=320). Without including the covariate, the ANOVA model and two of the main effects ...
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9 views

ANCOVA- Linearity with three CVs

I'm conducting an ANCOVA with a categorical IV (gender), obviously a DV and 3 CVs (one of which are also gender, but for a different group of population). I've tried assessing linearity for the three ...
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222 views

How do I understand ANCOVA in basic layman's terms?

I need assistance understanding the concept of ANCOVA in very basic layman terms. Also, can someone explain how ANOVA is different from ANCOVA: it seems both these techniques are used to compare means ...
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45 views

How to run a non-parametric ANCOVA in R?

I want to run a non-parametric ANCOVA in R and have come across the sm package and sm.ancova in R. However, I've been unable to ...
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Multiple Regression approach and ANCOVA approach to check for homogeneity of regression slopes

Hi i have a mixed design set of data with one continuous variable of satisfaction with 2 levels (pre- & post-) and one categorical variable of Service with 3 levels (S1, S2, S3). When running ...
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How to interpret a covariate in ANOVA and why are type II vs type III SS so different?

I am trying to understand the effect of a covariate (COVAR) in a linear mixed effects model with 2 categorical IVs (IV1, IV2). In order to illustrate where I am struggling, I had to paste the rather ...
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36 views

How to do ANCOVA in R

I have a plot of samples versus a number The red dots have been modelled with a red regression line and the blue dots with a blue regression line. I would like to compare the two regression slopes to ...