Questions tagged [ancova]

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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ANCOVA and moderator variables

I am currently doing research with an independent variable (four treatment groups), a continuous dependent variables, 5 control variables, and 2 continuous moderators. I figured out that I needed to ...
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Dealing with unequal measurements in MLM or ANCOVA

I am tasked with analyzing a preexisting dataset. The experiment is fairly simple, but I'm finding that analyzing the data is challenging due to the fact that the experimental design is not ideal for ...
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Is GEE a good replacement for ANCOVA to analyze change from baseline on 8-points Likert item?

I was asked to analyze adjusted change from baseline. The variable of interest is a customer answer reported on 8-point Likert scale, but constructed from numbers 0 - 8, rather than labels ("weak", "...
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When running an ANCOVA with two time points, how do you include a covariate that only has data at baseline?

I am running an ANCOVA where insufficiently active adults were recruited in self-selected teams (N = 24) to receive a web-based intervention with gamification component (TECH+C) or without (TECH). At ...
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ANCOVA or T tests?

I have data from a pre and post survey taken by adolescents who participated in a 10 month long pen pal exchange. The DV is their attitude toward people from other cultures. Covariates include gender, ...
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Difference between ANCOVA and Randomized Block ANOVA

What is the difference between an ANCOVA and a Randomized Block ANOVA?
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ANCOVA with two (related) factors

I'm analysing data from a repeated-measures study, in two participant groups (call them patient and control groups). I have measured a dependent variable response. Both the patient and control groups ...
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Should I use a GLM or an ANCOVA?

I'm studying leaf litter decay rates of two plant species, as affected by different treatments. As I need to compare the effect of the treatments, my director suggested me the use of an ANCOVA, with ...
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Differences in LSMEANS in R vs SPSS

I am trying to replicate results from SPSS in R. The model is a repeated measure ANCOVA. Funny enough: all the estimated parameter are the same (beta-coefficients, mean differences for contrasts) but ...
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ANCOVA with correlated predictors

I am doing comparisons between two groups---control and treatment---and would like to keep this question limited to the case of two groups, not the full-blown $k$-sample problem. In addition to ...
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ANCOVA baseline as covariate

just a simple question, to make sure this is correct. I watched some videos with similar study questions and I'm following them. I have 4 groups of treatments(Ct+A1+A2+A3), and two different moments, ...
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Paired sample, quasi-matched controls, and a covariate - ANCOVAs in R?

I have been going around in circles on this question for a while, so figured I'd resort to the expertise on stackexchange. My data: I have performance on a multitude of functional tests taken at 2 ...
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ANCOVA - adjusted dependent variable and t-test

I have a data set consisting of one independent variable $A$ with two levels/groups (e.g. patient = 1 & control = 0), continuous covariats $X$ and a continuous dependent variable $Y$. Here we ...
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Quantile regression ANOVA and ANCOVA [duplicate]

ANOVA posits that the mean of a particular group is equal to the overall mean plus some amount. If we find that amount to be significant, then we decide that the groups don't all have the same mean. ...
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Should you correct for group characteristics that are correlated to group membership

A little over a year ago, we have collected data by administering neurpsychological tests in several prisons (n=280). While this data is interesting by itself, we would like to compare these scores ...
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The Relationship Between Experimental Design and Non-linearity

It's well known that the classical ANOVA (and ANCOVA) experimental design techniques can be expressed as linear regression (with categorical factors). However, linear regression is just that - it ...
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Multi-leveled data, how to model?

I am designing biochemical analyses of human brain samples. In a nutshell, we believe levels of some things are related to levels of other things that relate to levels of other things that relate to ...
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Checking Heteroskedasticity in ANCOVA models : Breusch-Pagan test?

I would like to check the heteroskedaticity in an ANCOVA model : ...
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Multiple ANCOVAs: Post hoc Bonferroni, FDR, or can I use MANCOVA?

I am comparing a protein level in multiple (40 to 4000 depending on the analysis) brain areas across three diagnostic groups, with a couple of covariates. I am using ANCOVA to compare the three groups....
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Moderation and Ancova

I conducted a repeated measures anova with accent (British versus American) as 1 level and dress style (business, super casual, and business casual). My dv was how professional each was rated (1 to 7)....
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Determine influence of each covariate in ANCOVA

So I have run an ANCOVA with group (2 levels) as the fixed factor and accuracy as the dependent variable. I have 5 covariates, which I have entered into the model. After controlling for the covariates,...
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Change in X and Change in Y in Pearson Correlation

Suppose I have my x variable calculated as Hormone2-Hormone1 where Hormone2 is at a later time point and Hormone1 is earlier - this is true for all subjects and the time points are equally spaced for ...
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GLM Categorical IV Predictor vs Group by Analysis

I am modeling a continuous dependent variable with a couple of covariates (known a priori) and a variable of interest. I ran into an issue of interpretation which I'd like to clear up. When I ...
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independence assumption of ancova

Let's say I have a model with predictor A (with two levels, A1 and A2) and a covariate (...
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Understanding cov.reduce argument in emmeans function

I would appreciate any help regarding emmeans package. I am fitting dummy-variable regression model (ANCOVA) with follow-up post hoc test in ...
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Getting marginal means for ANCOVA in R (effect vs emmeans)

I'm a bit new to running GLM models in R, so forgive me is this is a silly question. Context: I'm running an ANCOVA with the goal to control for multiple covariates while understanding the ...
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3x2 within subjects design with covariate that is nested within factor (?)

I want to test the differences in my interval-scaled dependent variable - measured at three time intervals (within subj.), for two conditions (within subj.), while accounting for a interval-scaled ...
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ANCOVA: resolving hetrogeneity of regression slopes with multilevel modelling vs adding an interaction term

On the Wikipedia page for Multilevel model it is written that [M]ultilevel models can be used as an alternative to ANCOVA, where scores on the dependent variable are adjusted for covariates (e.g....
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Does it make sense to do Levene's test in relation to ANCOVA?

In relation to another question, Ben Bolker writes that if you have all-categorical predictors, you can test for heteroscedasticity (and other issues such as non-Normality) by dividing the ...
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Can I use a t-test to follow-up on a non-significant interaction in an ANCOVA?

I have an experiment that compares the impacts on students' learning (as measured by their performance on a pre and posttest) of two versions of a classroom intervention: D and R. I did an ANCOVA ...
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Negative coefficient in model caused by weak multicollinearity

I performed multiple regression and obtained the following model: Q = (0.33495)P + (-76.89321)G + (6.31424)P・G - 3.36334 P = precipitation; G = groundwater; Q = stream discharge The coefficient of (...
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Adding covariate to GLM

My response variable is a count data (vse23). My explanatory variables are a combination of continuous (zastska, razkrit, zastveg) and categorical factors (mezo). I did a GLM model of variables that ...
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What does it mean when running ANCOVA with two moderators and one of the interactions is insignificant when ran together?

I am hypothesizing that there are two moderators in the relationship between IV and DV. I ran one ANCOVA with moderator A and the interaction between IV and moderator A is significant. Then I ran ...
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Control for two variables in repeated measure ANOVA

I have a 2 factors repeated measure ANOVA for measuring Response Time to stimuli in two different contexts with two different stimulus types. The context and is not supposed to have any main effect. ...
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Am I Log Normalizing correctly?

I have searched the other questions about log normalization and all assume a level of understanding that I don't have. I have some ecological data and I am told that it needs to be log transformed. ...
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How do I conduct an ANCOVA within a pre and posttest design?

I have a question regarding the analysis of my quasi field experiment. I conducted an experiment in a high school where a class learns over 5 weeks with a smart personal assistant (n=22) and the other ...
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figuring out ANCOVA in R [closed]

I am not too familiar with using R for stats, but I really need to be able to analyze my data. I am comparing the level of a compound found in plants from two different locations, and within each ...
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Should I report the mean value of a DV before or after partialling out covariates?

I have the results of some ANCOVAS with 4 covariates. The mean value of the DV before and after partialling out the covariates is very different. Would you report both Mean values or just the one ...
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ANCOVA with Polynomial Categorical Variable

I have a homework problem that asks me to fit a one way ANCOVA model to a set of data (which I feel comfortable with). The model is represented as yij = μi + γzij + eij where i indicates ...
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How to transform a continuous variable which is a moderator in ANCOVA into a categorical one?

How do I decide where is the threshold to split it into levels? I ran an ANCOVA with a continuous moderator and it is significant, but I am wondering how to transform it to a categorical variable? Is ...
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Difference between MANCOVA and multiple ANCOVAs

I am analyzing the volumes of 13 different regions in the brain in a longitudinal (baseline and followup) study. I have two groups of participants - the therapy group and control group, and two time ...
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SPSS ANCOVA interaction significant once main effects removed

I'm running a 2x2 factorial ANCOVA, where the factors are either being in condition A or B and either being part of a certain group or not, with two covariates being age and gender. When I run the ...
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Within Correlation with ANCOVA or Multiple Regression

i have recently tried to understand a measure for within correlation from the paper (Bland & Altmann, 1995): https://www.bmj.com/content/310/6977/446.full The trouble is, the paper describes ...
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Pairwise comparisons of regression coefficients [duplicate]

I would like to know how to make quickly pairwise comparisons of regressions coefficients across three or more groups in R. Here is a small example: ...
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If change is DV and Pretest is covariate, should random effects take the form of (1|subjects) or (Pretest|subjects)?

I have Change from Pretest to Posttest (gain, no_gain, decline) as the DV. Pretest and Group as covariates. This called for a multinomial regression ...
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Account for covariate after predictor in ANCOVA?

I've been thinking about ANCOVA a bit and I didn't find anything on this particular issue. One of the most critical assumptions is that the predictor is not correlated with covariate (assumption of ...
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ANOVA OR ANCOVA?

I have 3 different groups of people that completed a language task. Some individuals took a drug and some did not. I would like to investigate the effect of the drug on performance in the different ...
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Ancova for unequal variances [duplicate]

What is the best way to compare two non-homogeinous populations (Levene's) with covariates (e.g. age). I know ancova assumes homogeneity. Is there a way around this? Many thanks
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How to calculte sample size of Mixed ANCOVA(2x2x2) using G*power

I want to know how to calculate the sample size of a Mixed ANCOVA model using the G*Power software. The study design is 2(between)x2(with-in)x2(between) and there ...
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Interaction not significant anymore in ANCOVA, but in ANOVA

I have a significant interaction $A\times B$ in my regular mixed ANOVA, but when I add a covariate, the effect $A\times B$ is no longer significant, but the interaction effect with the covariate $A\...