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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Am I running this ANCOVA correctly?

I'm doing a finger tapping study where there is a binary outcome (let's say "right" and "wrong"). I have a continuous variable (a kinematic measure from tracing the finger movements, "finger trace"). ...
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31 views

Multiple regression with an unbalanced grouping factor

I have a question regarding multiple regression with an unbalanced grouping factor. Essentially what I am doing is an ANCOVA, but the interaction term ends up significant (which is interesting!) so ...
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11 views

Allowed to do additional ANOVA after mixed-design ANOVA?

I have performed a mixed-design ANCOVA on cortisol values (in SPSS), with 'time' as the within-subject variable, 'group' as the between-subject variable and 'overall treatment time' as a covariance ...
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18 views

prove the effectiveness of a covariate using GLM repeated measurements

I do have a rather simple question but could not find a direct answer on other forums. I ran a repeated measures ancova with levels (2) as within-subjects factor on accuracy rates and entered age as ...
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2answers
22 views

ANCOVA Supressor effect?

I'm having a wierd kind of effect I don't fully understand when running an ANCOVA analysis. To keep it simple I have a variable X and a variable Y, these variables are significantly correlated to ...
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10 views

Performing Interaction Contrasts on mixed-models in R

I need to run interaction contrasts on the following data set. It is a mixed design with the dependent variable a questionnaire score measured across five test days (within-subjects variable 'Day'). ...
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5 views

3 groups, 3 measurement points, poisson distribution, baseline difference: GLMM or RM ANCOVA?

I have a small experimental data set. 3 group (n's = 12, 12, 16). T1 is baseline before intervention. T2 post-intervention, T3 follow-up (times between testing vary). The DV is count data that fits a ...
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1answer
19 views

How does ANCOVA increase the variance explained by the categorical predictor?

I'm reading Field (2013), in which there is an ANCOVA example with a categorical predictor Viagra, a continuous covariate, and a continuous outcome variable libido. I understand that in ANCOVA we ...
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13 views

Interaction with Continuous Variable and Between Subjects Variable

I am trying to test the interaction between three factors: One is a within subjects factor ("Scene Component": memory scores for difference scene component types: objects vs. backgrounds) One is a ...
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1answer
13 views

Does this qualify as a covariate in a RMANOVA?

I am confused as to whether a variable qualifies as a covariate in an RMANOVA. How can I find out and how do I use it? In a (hypothetical) within-subject, counterbalanced order, I present 2 memory ...
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13 views

ANCOVA model with non-significant variables performs better?

I'm running an ANCOVA test with 2 dichotomus and 1 ordinal variable as fixed factors and 2 continuous variables as covariates. I was advised to remove any non significant factors because with them ...
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29 views

ANCOVA with gain scores as IVs?

I ran an experiment (psychology) with two groups: experimental and control. I want to see whether the intervention changed the way in which participants habitually use some emotion regulation (ER) ...
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1answer
31 views

Two way ANCOVA with slight heteroscedasticity

I am about to perform a 2-way ANCOVA but I reject the null hypothesis in Levene's Test with a p-value of 0.023. See standard deviation and sample sizes below. I googled up and down and found people ...
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23 views

ANCOVA with binary response

I was wondering how I could perform an ANCOVA for a binary outcome variable - I have some factor and a continuous covariate that I want to account for in my model. How do I do that? Is there an ...
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13 views

comparison of Akritas et al's & McKean et al's nonparametric ANCOVA models & script of Akritas' model

I'm currently analysing the results of a pretest-posttest experiment with a categorical independent variable with four levels (three treatment groups and a control group) and a continuous dependent ...
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1answer
32 views

Difference between a random slope/intercept model and an ANCOVA with an interaction?

I attempted to run an ANCOVA with one binary predictor, one continuous outcome, and one continuous covariate. I found that there was heterogeneity of regression slopes and thus I concluded that an ...
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21 views

Selecting proper Linear Model with interaction considered

Data consists of Temp(3lv Factor), Water(num), Fert(num), and Growth(num). Considered model is LM with DV: Growth, IV: Temp with Water and Fert as covariate. Fitted 2-Factor ANCOVA (Full Model) and ...
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19 views

ANCOVA with small group size

I have one independent categorical variable 'A' with five groups (n = 1, n = 2, n = 9, n = 18, n = 20). Then I have a continuous dependent variable 'B' and a continuous covariate 'C'. I want to ...
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2answers
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ANCOVA intercepts - does R center data?

I have 2 fixed effects and 2 continuous predictors. Nothing interacts so I believe I want a model of the form: $$Y_{ij} = \mu + \tau_i + \beta_j + \gamma_1(X_{1ij}-\bar{X_1}) + ...
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28 views

questions about ancova model with both random and fixed effects

I have the following data (I show part of the data below) and would like to consider the ANCOVA model with type (a factor with levels 1 and 2) a fixed effect and batch a random effect nested within ...
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26 views

What's the difference between including a variable as a mediator in a mediation analysis, and including a variable as a covariate in ANCOVA?

I understand that ANCOVA has a continuous outcome variable, and a categorical predictor, and (at least) one continuous covariate. Can this be run as a mediation model instead, and if so what are the ...
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32 views

repeated measures ANCOVA; covariate main effect and post-hoc tests

let's say I run a repeated measures ANCOVA, with valence (negative and neutral) as repeated measure and age as a covariate. what I want to know is how age affects my data. 1)I get a significant ...
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1answer
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How do I statistically test whether two intervention types have significantly different effects in a meta-analysis?

I have the following problem: I am researching the difference in effects (as measured by standarized mean differences (SMD)) of two intervention types. (let's call them intervention 1 and intervention ...
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Can I use a covariate in a RM-ANOVA design and can the covariate be ordinal?

I'm having some trouble deciding what the best approach is to may data. The following is the setup of the study: Between-subjects factor: Group (2 levels) Within-subjects factors: Time (2 levels), ...
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33 views

Should I include weights in LME?

I have two case studies where I am looking at the influence of a trait (trait A) on mortality (m) of trees and seedlings. Following your comments on ...
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46 views

Anova (missing F statistics), Ancova and mixed modelling on nested dataset

I am performing an analysis in R and wonder how to do it since different methods return very different results. My dataset contains Samples and SubSamples as nested random effects and Type, Dose and ...
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1answer
28 views

ANCOVA - F notation - very simple question

I can't understand the number with the F value ($F_{2, 89} = 0.93, p = 0.09$) in result section from the following paper. Relevant section is quoted below. Can anyone please explain this to me? ...
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1answer
41 views

ANCOVA or not? Non continuous covariate

I have done an experiment with an independent and dependent variable. I repeated the experiment 5 times. Obviously all the repeats will be different from one another, some of them significantly so. ...
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42 views

Confused about whether to use t-tests or ANCOVA or ANOVA

I am investing whether vitamin C supplementation can attenuate creatine kinase increases after a strenuous workout. My participants are divided into two groups, VitC group and a Control (no ...
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20 views

Wild bootstrap in “bordeline" case t-test

I have to compare the mean levels of a continuos variable y (ranging 1-20) subdividing my sample in two groups according to a dichotomous variables (i.e gender). Sample sizes of the two groups are ...
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33 views

Repeated measures ANCOVA

I have a data set with training effects and I measured the outcome variable before, during and after training. This is a repeated measures design and I hope to find an effect of training on the ...
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28 views

Is Wild Bootstrap a good strategy in General Linear Model (ANCOVA) with Assumption Violations (both normal residuals and homoscedasticy)?

I need to perform several GLM's (i.e. ANCOVA’s, with a single continuos dependent variable and several predictors, one dichotomous and some other continuos). I was looking for both a significance on ...
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30 views

Test for ANCOVA validity in R

I have a function Y ~ X + trt; where for each trt (treatment group), I have Y and X which correlate with one another. Basically, I want to use ANCOVA to estimate the model parameters, but I don't ...
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1answer
35 views

Sampling intercept and slope pairs from lm in R

Let's say I have a model Y~X+trt, and by running lm and summary functions in R I get these results: ...
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25 views

How can I make an ANCOVA in R (Prior to a Cox ph model)?

I want to make an ANCOVA analysis of the survival rate of flies after being on a bad diet for the first 21 days of their lives compared to those always on a normal diet. I have studied the responses ...
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1answer
54 views

Controlling nuisance covariate in lmer

I want to control for a nuisance covariate in a linear model. Since the covariate interacts significantly with one of the fixed factors, the homogeneity of regression slopes assumption is violated for ...
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40 views

Pairwise comparisons with covariates

I have a simple ANCOVA model such that outcome ~ sex + group with outcome being continuous, ...
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How should one incorporate multiple forms of information about a single variable into a model?

I sincerely hope this is a question that can be definitively answered! I'll do my best. Let's say I have two treatments, flower removal and defoliation, that are fully crossed in an experiment, and ...
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54 views

Longitudinal pre-post test/follow up

I am an undergrad student trying to get my head around statistical analysis. Can someone help me to make sense of the best way to analyse my data? ANOVA, ANCOVA, t-tests....it is all a foreign ...
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1answer
160 views

Ancova Levene's test significant

I did ANCOVA with Depended: Posttest/ Fixed: Group/ Covariate: pretest Levene's test is statistically significant: .002 Is the assumption of homogeneity of variance violated? If yes , what can i do ...
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17 views

Repeated measures ANCOVA - heterogeneity of slopes

In my 2x2x2 mixed model ANCOVA, the covariate is interacting with only one of the main effects (repeated measures). Would it be OK to interpret the rest of the effects and interactions (which were not ...
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44 views

ANCOVA; CIs for the intercepts of each treatment

I am currently doing an ANCOVA, and I need to calculate CIs for the intercepts of each treatment (categorical) group. So, instead of using lm(y~x+group), which gives me SEs of treatment contrasts, I ...
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I want to compare two calibrations with R… But cannot find the right answer

I first want to precise that I spent 2 hours searching for an answer, couldn't find something that was answering my question. So basically, I ran two calibration with my diagnostic test, so I ...
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1answer
26 views

interpretation baseline corrected ANCOVA

I hope you can help me with some statistic 'problem', or maybe check is more accurate =]. I have data on an experiment with a 2 by 3 design, with session(first/second) and medication(a/b/c) as ...
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Is it necessary for covariates in an ANCOVA model to be normally distributed? [duplicate]

I am running an ANCOVA model and am trying to remain true to all the statistical assumptions. I noticed that one of my covariates is not normally distributed, I know that the X and Y variables should ...
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1answer
151 views

Using ANCOVA when the covariate is not normally distributed

I have conducted a repeated-measures ANOVA, but a reviewer suspects that the observed main effect of condition are due to a the difference between hit rates of two conditions (one of them is ...
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30 views

Nonlinear form of ANCOVA?

I would like to compare a control group against a test group using something like ANCOVA. However, the covariates are not simple, as some items may have already been increasing with time, others ...
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Running 2x2x2 ANCOVA in SPSS

I need to conduct an ANCOVA on my data. While I've taken a number of statistics courses, I have never come across ANCOVAs and I want to get some feedback on the correct way to conduct this analysis. ...
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how to analyse an interaction in a within-subjects repeated ANCOVA post-hoc?

I have pre and post measures of attention that I am examining in a within-subjects repeated measures design. I wanted to check the effect of verbal intelligence [VIQ] on my attention[pre/post] ...
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What can be done when a covariate was influenced by the experimental treatment?

I have a problem regarding my data for an ANCOVA. I conducted an experiment with a 2x2 between subjects design (4 different treatment groups) and covariates. Due to the treatment I was just able to ...