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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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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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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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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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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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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Interpreting interaction effect with orthogonal polynomial contrast codes

I'm running a logistic regression with two categorical variables (sample_number: 1, 2, 3, 4; and sample_length: 60, 70, 80, 90, 100) and a continuous predictor (dot_size). My model in R looks like ...
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Control covariates in paired t-tests (pretest-posttest design)

Suppose we have a naïve single-arm pretest-posttest design without any control group. Every subject has a pretest score and a <...
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Is it ok to drop a non-linear treatment level in ANCOVA?

I am running an ancova to measure differences in an allometric relationship between tree height (dependent variable) and diameter (covariate) among one nutrient treatment with 4 levels. One of the ...
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Appropriate model choice for analyzing many repeated measurements in the context of a parallel arm randomized controlled trial

Background I am conducting a parallel-arm randomized controlled trial comparing Treatment A against a Control. Each week for 10 weeks I measure anxiety in each group each week (giving a total of 10 ...
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ANCOVA (or other model) with non-parametric data distributions in R?

I am working with a dataset collected from human subjects that has 46 continuous dependent variables, one categorical independent variable with four groups (n = 20-30 per group), and three covariates (...
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How to determine if one variable affects the relationship between two separate variables

I have a dataset where two continuous variables are almost perfectly correlated. There is a third categorical variable and I need to perform a statistical analysis to determine if the categorical ...
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Why type III sum of squares is not recommended to use when there is significant interaction?

I did notice that in the following example, I obtained a insignificant main effect for treatment when including interaction, although the treatment is clearly effective. Any intuitive explanation? ...
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Different ways to include pre-test performance as a covariate in a linear mixed-effect regression. Which is correct?

I have a pre-post experimental design, where I have measured participants' performance in three courses (tasks; A, B, C) at both pre and post-test. The study is a learning experiment. 60 elite alpine ...
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Should I use an ANCOVA test?

For this data set: I want to see if the DNA levels differ if there is food or no food and if this changes due to the number of days. Does it make sense to use ANCOVA as the Age could be considered a ...
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Effect of getting closer to a normally distributed covariate on result of ANCOVA

I have a question about ANCOVA. We did an experiment with 2 groups and then calculated an ANCOVA to see if the DV differed between the groups. We included one binary and one continous covariate (PO). ...
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Can this be classified as an ANCOVA?

ModA <- lm(Temperature ~ Section*sin(2*pi*t)+Seccion*cos(2*pi*t),data=MyData) ModB <- lm(Temperature ~ Section+sin(2*pi*t)+cos(2*pi*t),data=MyData) I have to ...
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Covariate analysis comparing distributions / means of circular data

Are there publicly available software packages to run an analysis comparing the means or distributions of two samples of circular data with the presence of a covariate? If not, are there ways to ...
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ANCOVA when continuous predictor is a main factor of interest: extension of a related post

From the literature, I understand that we often assume an ANCOVA is only useful for "controlling" for covariates. However, from this related Stack Exchange post, an ANCOVA should also be ...
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2 votes
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Multiple correlated outcomes in a randomized experiment with two groups and two time points: How to analyze?

In a randomized trial, subjects are randomized into two groups, a control group and an intervention group. There are multiple outcomes (15 in total), namely miRNA (microRNA) which are measured before (...
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Hurdle model: How to compare slopes?

I'm analyzing the change in seagrass cover (count data of shoots) between two years of different species. Therefore, I made a model similar to this: ...
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Baseline adjustment when both pre- and post values are subject to left-censoring

Assume $X$ is a binary treatment variable, $Y$ is a continuous variable measured pre- and post-treatment $(Y_{pre}$, $Y_{post})$, and $Z$ represents the remaining covariates. Both $Y_{pre}$ and $Y_{...
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Leave out non-significant covariate [duplicate]

In my study, I make use of two covariates. After running a two-way ANCOVA in SPSS, it turns out that only one of the two covariates is significant. Should I remove the one that is not significant, and ...
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GPower: Difference in Sample Size for ANCOVA vs. Repeated Measures ANOVA in clinical trials

I want to conduct a randomized pre-post intervention study with two measurement points (1. Baseline 2. Post-intervention) and two groups (Treatment vs. Control) and am currently trying to work out the ...
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Query regarding Models in MANCOVA?

This is the query in the area of Mancova in SPSS. There are 8 dichotomous IVs and 7 DVs. IVs are shape components of the bottle like deep curve, slim, parallel etc. and DVs are like sophisticated, ...
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Interactions and/or covariates for a regression in r

I have to find the regression between to continuous variables, and this I have done with an lm() in r. Now I want to test if a 3rd variable is a covariate, the variable is size and it is also ...
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How to statistically account for the different length of time patients were on the different drugs, as to compare the two groups in R?

Conducting a statistical analysis of two groups of subjects being on different drugs. One group has stayed on drug A, while the other group switched to drug B from drug B at around the middle of the ...
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What statistical method would I apply?

Basic information for my project is below; RCT Group(3); A type Exercise, B type Exercise, No(Control) Time(3 times measurements); baseline, 4wk, 8wk Outcome; mental health (continuous variable) -...
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What statistical model should be used to analyze data from a randomized pretest-posttest controlled trial when subgroups exist?

I'm planning a randomized pretest-posttest controlled trial of a psychological therapy intervention group compared to an active control group on a dependent variable of interest. My population will ...
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Analysing a controlled pre-post intervention study

I am conducting an analysis involving a non-randomised group of 30 individuals who received an intervention with the purpose of improving medicines regimes and a matched 1:1 control group as part of a ...
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