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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Multiple Regression: 3 groups for IV, post-hoc equivalent?

I would like to test the following: DV - Brain volume IV - Participant Group (Patient with Mild Symptoms, Patient with Severe Symptoms, Controls) Covariates - Age, Gender, IQ I wish to use ...
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3answers
153 views

Do I have a justified reason to exclude a non-significant covariate from my ANCOVA? How interesting is unequal variance?

I am comparing glutamate concentrations across groups (2 groups). I planned on controlling for age and IQ, simply because this is what is always done in cognitive neuroscience. When doing this, age ...
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19 views

Clarification on the comparison between regression lines

I have this dataframe: ...
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10 views

What analyses do I run for a 1 x IV; 2 DV's; and 2 x timepoints?

I am looking to run an analysis that has: 1 x IV (group type: control vs intrevention) 2 x DV's (Alcohol Consumption, and Modelling Behaviour) 2 x Timepoints (Baseline and 1month follow-up) I was ...
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20 views

Which statistical method can I use to see if there is a correlation between data sets with different size?

For my thesis I want to compare the 3 different test results. If the results are more than 5, samples are failed. And I want to show if these tests are similar behaviour (if there is a correlation ...
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8 views

Two-way ANCOVA with count data— Poisson model in SPSS

I am attempting to compare the number of eating episodes by gender and diagnosis (4 levels), adjusting for BMI and age. I am assuming that a Poisson model would be preferred over a factorial ANCOVA ...
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14 views

Multiple categorical and continuous variables in ANCOVA

I have performed an experiment where insects in a certain order were captured and identified at set distances from a forest boundary. At each point I have measured a number of environmental variables ...
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18 views

How to choose variables to include in ANCOVA

I have a data set that includes a DV (Richness or Abundance) and multiple continuous and categorical variables: ...
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29 views

ANCOVA without between subjects factor

this might seem like a stupid question but my knowledge of statistics has become fuzzy over the years. I would like to perform an ANCOVA without using a between subjects factor. Is that possible? I ...
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1answer
18 views

How to address unintended confounding in an experiment

I am conducting a study looking at the effects of 3 different footwear conditions on energy expenditure during running. This will be a repeated measures study. I want to control for the effects of ...
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17 views

Polynomial ANCOVA glm in R

I have a data set of success and failure counts with one continuous independent variable and one factorial variable: ...
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1answer
31 views

Comparing correlation between groups

My data looks like this: ...
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48 views

What statistical approach to use for this kind of analysis?

I have 1 dependent (continuous) variable, 3 explanatory (continuous) variables and a bunch of control variables. The explanatory variables are my interest variables.I want to do a categorical ...
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15 views

removing the effect of a categorical variable in a linear model

I would like to remove the effect of a categorical variable from a linear regression model. A simple example could be the following: outcome ~ beta0 + beta1 * dummyIsFemale + beta2 * ...
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14 views

Graph output from non-parametric ANCOVA

I have a small dataset consisting of a control/impact setup with 11 samples each. A low number of samples with a nonlinear setup pushed me towards a non-parametric ANCOVA, such as from the 'sm' ...
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4 views

How to account for individual covariate values in an analysis of covariance (ANCOVA) in SPSS?

By default the estimated marginal means (also known as covariate-adjusted means) in SPSS saved from an ANCOVA model are calculated using the grand mean values of the covariates. However I would like ...
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1answer
32 views

Can we make mediation analysis with ANOVA?

I conducted mixed ANCOVA for my research. However, I need to make a mediation analysis as well. I have no idea of converting a mixed ANCOVA with many control variables into a regression. Can't I do ...
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26 views

Control for regression to the mean effects when comparing propensity score matched observations?

I'm working on a project where I'm comparing the % change in total annual health care expenditures among patients who did or did not participate in a cost reduction intervention program. We're ...
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7 views

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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40 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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17 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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19 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
26 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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16 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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19 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
23 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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40 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
15 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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17 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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32 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
44 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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32 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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19 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
50 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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22 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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20 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
87 views

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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35 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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42 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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51 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
58 views

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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45 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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51 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
34 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
60 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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51 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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22 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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47 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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37 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 ...