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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Treatment Effect in a clinical trial

We have a randomised controlled trial, with two groups of the same size (drug and placebo). A variable was measured before and after substance administration. To assess a treatment effect, two ...
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Quade test in R [on hold]

I would like to perform a Quade test with more than one covariate. My question is if it is posible to use more than one covarite in the Quade test. If the answer is yes, I would be pleased if you ...
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1answer
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Is it possible to compare 2 groups while controlling for something?

Is it possible to compare two groups (e.g., t-test, Wilcoxon, Mann-Whitney test, etc.) while controlling for something? E.g., I want to compare home ownership between military veterans and non-...
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1answer
51 views

Using lme to perform a nested ANCOVA in r

I want to perform a nested ANCOVA using the function lme in r. My data concerns the growth rate (sgr) of fish at different temperatures (temp). In the trial there were 3 replicate tanks each housing 8 ...
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covariate in ANCOVA

I have two groups I want to compare- drug and placebo- on a few dependent variables from neuropsychological tests. I ran a MANCOVA using only one covariate (related to the DV) and I found two out of ...
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2answers
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Is ANCOVA correct here?

I am analyzing data from a mindfulness intervention in which 60 participants took part in an ipod-based intervention listening to meditation tracks. Outcome measures on anxiety, depression, stress, ...
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Difference in performing two-way ANOVA and one-way ANOVA

I was asked by reviewers to retest my hypothesis that states A1 is better than A2, B1, and B2 (2x2 factorial design where A/B are two levels of the first factor and 1/2 are two levels of the second ...
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1answer
64 views

ANCOVA interpretation – inconsistency between ANOVA results and pairwise group comparisons

I have some measurements (concentration) made in 4 groups (W, X, Y, Z) and time is my covariate. I make a linear model: ...
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1answer
62 views

Repeated measures study with a covariate

We conducted a study where we are measuring perceived tiredness at different intervals (a total of 10). We recorded a score before starting the experiment, as a covariate to account for differences in ...
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Mean sum of squares and products according to source of variation in ANCOVA from R

How to get the mean sum of products using R to populate an ANCOVA table as given in the following link? Analysis of Covariance Table for RBD Ryy, Tyy and Eyy can be obtained as follows using ...
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4 groups | 3 measurement points | SPSS

We are performing a RCT with 4 groups (1 control + 3 experimental), where we measured physical activity (PA) in 3 moments (at baseline, post-test and follow-up). Although we have done stratified ...
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ANCOVA for 2X2 crossover with baseline measurements - validity of assumptions

I'm trying to learn how to do ANCOVA for a 2x2 crossover study with baseline measurements. I have followed the analysis performed at Mehrotra 2014 "A recommended analysis for 2 x 2 crossover trials ...
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SPSS | Repeated-Measures ANCOVA | Covariate

We are performing a RCT with 4 groups (1 control + 3 experimental), where we measured physical activity (PA) at baseline, post-test and follow-up. Although we have done stratified randomization, the ...
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Why do we need to check for these two assumptions for ANCOVA but not for factorial ANOVA?

ANCOVA has two additional assumptions as compared to two-way factorial ANOVA. They are (1) independence of the covariate and factor (2) homogeneity of slope. Why don't we need to check them for two-...
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24 views

how to report the comparison of two samples means, accounting for covariates

I have two groups, patients & controls, and a dependent variable "performance". I want to compare the means of the two groups, but after removing the effect of two confounding continuous ...
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15 views

Before/After analysis + controlled variable SPSS. ANCOVA?

I am using trip data from NYC's yellow cabs and the newly introduced citibikes (bikesharing system) in 2013. I have frequencies etc. of the taxi's before and after the introduction of citibike. I ...
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28 views

ANCOVA with ordinal covariate?

My study looks at the effects of sex on performance in a psychological task. There are 3 variables: sex (m/f), plus 2 within-subjects factors (with 2 and 3 levels), so it's a 2x2x3 repeated-measures ...
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27 views

How many df in ANCOVA?

I am trying to run an ANCOVA with interactions in R, with 2 categorical variables (2 levels for each) and one continuous variable. The model is x~y1*y2*y3. The output in R (aov, type=3 via the "car" ...
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1answer
106 views

Mixed-effect model / ANCOVA with lmer in R

I have a question according the following example: What I want to find out is whether two fertilizers (A and B) have different effects on the biomass of my plants. My explanatory variable is '...
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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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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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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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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 2....
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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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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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1answer
22 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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1answer
28 views

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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19 views

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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29 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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20 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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26 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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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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ANCOVA interpretation

I have a continuous independent variable (AGE_CONT), a categorical independent variable (EXP_CATER, within subject, three ...
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1answer
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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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1answer
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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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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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42 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
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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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47 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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1answer
29 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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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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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, ...