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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GLM: how to treat multiple variables that all measure a confounding aspect in a slightly different way?

For a response variable $y$ and predictor $x_0$, I have data for a number of additional variables $x_n$, $n = 1, ..., 7$. I would like to control for a confounder in my GLM, let's call it "size&...
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Understanding impact of significant covariable on treatment (ANCOVA)

I used paired sample t-tests to show significance on three dependent variables with one independent variable. All were significant in the experimental group and not in the control group. I controlled ...
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ANCOVA with two dichotomous IV and three covariates - how to interpret interaction between IV

As part of my thesis I am investigating how emotions influence food preference predictions between romantic couples. I've run an ANCOVA with one continous DV ...
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What type of analysis to use for a pre-post test design with paired means and covariates (stata)

I am conducting a retrospective analysis of the efficacy of an intervention with "Therapy A." There is a baseline period and a treatment period, however, all the patients received the ...
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1 answer
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Justifying a smaller control group in survey study

I am planning a set of studies that are interlinked. The first study collects information from 400 participants (exposure group), then some psychometrics are performed to assess the questions. In a ...
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ANCOVA with all continuous variables

I have the following variables: Psychological trait data collected at pre- and post-intervention Fitness data (e.g., weight in kg), collected at pre- and post-intervention I am interested in seeing ...
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What sort of test to use when the ANCOVA has a categorical DV?

I am carrying out some research, and I realised that my DV is going to be categorical. I originally planned on carrying out an ANCOVA; I have 1 IV with three levels, 1 DV and 4 covariates. After doing ...
2 votes
1 answer
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Is it okay to leave a treatment group out of an analysis?

I am currently analyzing data from an RCT. The primary findings from the RCT have been published and we are now examining the data further. In brief, the RCT examined the effectiveness of a new ...
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Mixed ANCOVA SPSS Interpretation

Before I ask my query I need to explain some basic details with respect to my study. Design: I have a mixed factorial design 2X2x2 with two within subject factors (having 2 levels in each factors) and ...
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1 answer
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Repeated measures ANCOVA interpretation – significant covariate/test day interaction

I am in the last phases of my master’s thesis, and came across a question regarding my data analysis results that I cannot seem to find a clear answer for. For context, my data is from a randomised, ...
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Do there exist welch's repeated measures anova/ancova/manova?

Do there exist welch's repeated measures anova,ancova for unequal variances or does one have to run a mixed-effects regression or friedman test? Is it possible to generalize this methodology to ...
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Is it justifiable or acceptable to only check for moderation only in the experimental groups not in the control group

controlled experiment we have 5 groups: 2 Control Groups (CG, passive and active) 3 Experimental Groups (EG, Doseage of the Intervention). We also have two measurement time points T1 and T2 and ...
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ANCOVA vs linear mixed model in R, using different functions gives me different results

I have tried different packages, functions, libraries etc in R and my results differ, whether it be p values or F values or DF etc. This is especially true for my within variable (hemi).. between: ...
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Linear Mixed Model with repeated measure design, continuous and discrete predictors, and continuous predictor partially nested under discrete factor

Let's say I have the following data frame where subject ID (random factor) is completely crossed with the two other factors: IV1 and IV2. Additionally, IV2 is partially nested (or partially crossed) ...
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Can I do an ANOVA while controlling for a categorical variable (an ANCOVA except the covariate is categorical)

I'm looking at nesting differences between 3 species of fish. These fish nest in colonies (all 3 species intermix in the colonies), and measurements were taken at several different colonies throughout ...
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Simple regression on subsets vs ANCOVA with interaction term

I'm attempting to predict a continuous variable as a function of one continuous variable and one categorical variable. This led me to an ANCOVA, but I've violated the homogeneity of regression slopes ...
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RCT with missing follow-up outcomes: ANCOVA + MI vs Mixed-Effects Modelling?

In a 2-group RCT with one baseline and 2 follow-up assessment time-points, assume that (i) follow-up outcomes are missing at random (ii) relatively strong auxillary variables are available My question ...
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Next step after ANCOVA assumptions violation

I'm analyzing the heart rate response of a sample of individuals to three tasks. Each individual performed all three tasks I was recommended to do an ANCOVA with time to complete task as a covariate ...
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How to interpret the R output for repeated measures ANCOVA?

I conducted a repeated measures ANCOVA in R using this code: rm.model <- aov(c.se ~ RA01 + Error(id/time) + c.age, data = repm) I got following output: Output R-...
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Assumptions of repeated measures ANCOVA in R?

I have a randomly allocated control and experimental group, as well as pretest and posttest. To control for baseline differences, I saw that conducting an ANCOVA is recommended. However, two ...
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What are the assumptions of repeated measures ANCOVA?

In my experiment I have a randomly allocated control and experimental group, as well as pretest and posttest. To control for baseline differences, I saw that conducting an ANCOVA is recommended. ...
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ANCOVA - Follow up tests

Which follow up tests should be used with an ANCOVA to make sure the covariate is included in the assessment ? I’m struggling to find an appropriate test for this.
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Z-scores and comparisons of means

I am interested in comparing mean protein levels (dependent variable) across four groups (independent variable), while controlling for covariates/ confounders. I will perform this (essentially ANCOVA) ...
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Appropriate test for categorical independent variables with sub-level

I am stuck on how to analyse my data. I have one dependent variable and a number of indepen dent variables which are divided into further sub-categories. Some of the options for the value of an ...
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Question about deciding whether something is a moderator or covariate

Based on what I know, a moderation analysis is simply looking at an interaction between an IV and a moderator. However, people often refer to moderators when they talk about ANCOVA (analysis of ...
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On the defense of "change from baseline" even in randomized trials - can anyone question points in this article?

Many times I read a strong criticism on the change-from-baseline (adjusted for baseline or not) both in randomized and non-randomized. Several people advised "don't even think of reporting the ...
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How to quantify the effect of a mediator, SPSS, Psychology experiment

I have collected data to answer the question “Does Neuroticism Mediate the effect of a Mindfulness Intervention?” I Have collected pre-intervention Mindfulness Score and a post intervention measure (...
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Analyzing data from a pre/post study when ANCOVA isn't possible and the denominator may be zero when calculating change scores

We have conducted an experiment on an animal model of a psychiatric disorder using a pre-treatment (PRE)/post-treatment (POST) design with two treatments resulting in 4 study groups (No treatment, ...
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Calculating fixed effects in a mixed model with non-normality and heteroscedasticity with a 3-level time variable?

Due to non-normality and heteroscedasdicity, I use robustlmm and not lme4 for my mixed effects model. The variables look like this: ID: subject variable (random factor) var1: categorical between ...
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How to represent ranked ANCOVA in a violin plot?

When I did ANCOVA, I did not find normality and equality, so I did ranked ANCOVA(nonparametric tests) using SPSS. well.. I think that if I use just ANCOVA(parametric tests), I could create the violin ...
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Predicting an interaction between a covariate and an IV in a fully within-subjects design

My design is 2x2 repeated measures ancova, and I'm predicting an interaction between one of my within subjects independent variables (IV) and a fixed covariate (CV). My question is what this means for ...
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ANOVA or ANCOVA? I have a control variable

In my study, I am analyzing 4 groups, as it is a 2 (primed or not primed) × 2 (high efficacy or low efficacy) experimental design. I am planning on using ANOVA between-subject analyses to test for ...
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What to use for nested subjects with repeated measures, ANCOVA or LME or even SEM?

I have a dataset like: I grouped the subjects based on their initial depressive mood (first step (pre-treatment) of repeated measures level) as 1 low, 2 high. I have two conditions (1 control, 2 ...
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Adjust outcome variable values dependent on a factor

I am running an longitudinal study on electricity consumption. I test the effect of 3 interventions on DV consumption in kWhs. For the interventions, I have a categorial dummy var with 3 levels. I run ...
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Correct way to make ANCOVA in R for RCT

I know there is already some information on the subject but I find different variantes, do not quite understand the differences and their effects and want to make sure I do not make a mistake. I have ...
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2 answers
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ANCOVA limitations and alternative methods

I was given a database with prostate cancer patients measured for PSA (continuous) at two time points, prior and after treatment, using three drugs (categorical), including information about age (...
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ANCOVA with common zero level

There is a similar, if not duplicate, question from 9 years ago on this but it never got answered so I'm hoping to get some clarity on this. Let's say we have N ...
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How to test for difference between two GLMs (generalized linear model) in R?

What are appropriate tests for determining whether two GLMs are statistically significantly different? AIC and BIC is not an option because I am not trying to determine parsimony. If it were regular ...
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are mixed ANCOVAs possible?

I am trying to figure out which type of ANOVA I should be running for my experiment. I have 5 watering treatments, and each type of treatment has 6 plots. I measured the percent plant cover of each ...
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How can I find out if an interaction between one categorical variable and one continuous variable has an effect on another continuous variable?

First, I know just little about programming and statistics. For this assignment I got a table with gene expression values (continuous data) for 3 environments (1, 2, 3 so categorical data) with ...
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The homogeneity of regression slopes assumption 2 way ANCOVA with 2 covariates in R

I have a dataset with a DV, 2 IVs(IV1 & IV2) and 2 covariates(CV1 and CV2), and I want to compare means of the DV with 2-way between-group ANCOVA using the covariates in R. But I'm not sure how to ...
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Statistical test for injury data

I have patient mental and physical health scores and looking for differences pre and post injury. The injuries are categorical by anatomic site and severity. I was told to run a GEE with Walds test ...
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Comparing slopes for 2 datasets - ANCOVA or something else?

I am looking to determine whether two slopes (linear model) are statistically significantly different (p-value) from one another. Inserted is a graph showing the data and below is a toy version of the ...
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How do I obtain regression results from a 2-way ANCOVA with a random effect (linear mixed model) in R?

My dataset includes the following variables: Response variable - respiration rate (continuous) Regression variable/covariate - weight (continuous) Explanatory variables - temperature (2 levels: high ...
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1 answer
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Accounting for Categorical Covariates in R

I am conducting a study looking at the interactive effects of delay group (12h sleep, 12h wake, 5min AM, 5min PM; between subjects) and study condition (reread, practice test without feedback, ...
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Which mixed-effects model would give what I want to analyze?

I have a repeated measure design and also a group variable. I would like to analyze how the difference between first measurement and second measurement of the repeated measures (depression) explained ...
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1 answer
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ANCOVA by SPSS with outliers and non-homogeneity

I’m working on ANCOVA to compare post- vs. pre-treatment percentage change of a blood test value, L, between 10 groups (10 dosages from 3 drugs all of which can lower L), with the pre-treatment (...
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Confused by post-hoc comparisons for ANCOVA using either SPSS or R

I ran a two-way ANCOVA with two covariates and would like to run post-hoc comparisons that generate a p-value (the interaction was significant). I'm running into trouble in SPSS, because adding ...
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Compare the slopes of two linear models in R

I have two linear models. m1 <- lm (y ~ x) m2 <- lm (y ~ z) My goal here is to see if there is a significant difference between the slope of the two models. I tried ANOVA but was unsuccessful. ...
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1 answer
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Omnibus test significant but no individual factors are significant [duplicate]

I'm running a multiple logistic regression in R. Im predicting whether or not a stimulus was seen from the number of dots in the stimulus (sample_numerosity; 4 ...

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