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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Questions concerning visualizing model results with the R-package visreg

Following some discussions with colleagues, I'm seeking for clarification on how to visualize an ANCOVA with visreg, and what the visualization actually shows. I would like to run the following ANCOVA ...
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Age matching in three group ANCOVA design

I have to compare two groups of patients who are defined based on their chronicity of illness, hence of two different age distributions. One group is younger on average and the other older. I would ...
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Which type of sums of squares does lm-function in R use?

I ran a two-way ANCOVA in R: ancova = lm(DV ~ IV1*IV2 + CV1 + CV2 + CV3, data = Data) summary.aov(ancova) Anybody know if this uses type III sums of squares? I ...
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What type of analysis to do for Dissertation- EMOTION RECOGNITION

In my study, participants take part in the State Trait Anxiety Inventory (STAI) where they are ranked into high or low trait anxiety groups. Participants are then shown multiple videos of 7 different ...
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Why not accounting for a factor unrelated to treatment makes p-values too conservative?

I would like to know if a treatment works, but different subjects are measured across different sites. The site is unrelated to treatment, but it is related to the response (see the figure). If I put ...
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How to test the null hypothesis that two linear regression lines have the same Y value for a particular X value?

I am using ancova to test if two linear regression models are the same and it works great. I am following this tutorial: http://www.biostathandbook.com/ancova.html and I apply it in R with this ...
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Non-parametric equivalent to ANCOVA

I would like to do analysis with co-variate. However, some of my data is skewed and has outliers, so I would like to use non-parametric approach. The issue is that, I could not find any non-parametric ...
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How to look covariate for treatment between patients and controls?

I have this study where we have 2 patient groups, both on a the same medication (for ethical reasons, patients had to remain on their medication), and 1 control group. There are significant ...
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Mixed ANCOVA: What to interprete?

I've used several statistics packages to run a mixed ANCOVA with one within-subjects factor, one between-subjects factor and one covariate and I am confused as the output produced varies. When I run ...
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GLMM appropriate for constant covariates/ baseline score? Or Ancova?

I was wondering whether my data is appropriate to fit a glmm (with r package lme4) So, I measured a questionnaire two times (q1 and q2). Also, I have variables ...
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Analysis of treatment effect with partially non-randomized groups

I have conducted an experiment in which participants were randomly assigned to six groups: Control group Control group with additional information about problem Pre-set treatment group Pre-set ...
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How to control for a categorical confounding variable in statistical analysis without using parametric tests?

I have around 150 variables of psychometrical data for 97 subjects (Scores and percentages of tasks, Reaction Times, and Factors, such as social-economical status of participants). The goal of our ...
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ANCOVA for finding relationship between 1 categorical, 1 continuous IV and 1 categorical DV?

I have collected crime data from a few different sources. These sources label crimes differently, and I would like to see if I can safely combine any categories from the different datasets. For ...
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ANCOVA controlling baseline in RCT - power analysis and sample size questions

I am performing a power analysis/sample size estimation for an RCT. We will be controlling for baseline symptoms and using post-treatment or change scores as our outcome variable. This design is ...
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Would very small stratum be a problem for ANCOVA model?

I know that for logistic regression, if you get an empty cell, the model may not run at all. How about continuous outcome? If one of the categorical predictors has very small stratum, would there be a ...
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Repeated measure ANCOVA query

My participants are allocated to an intervention A or B. Participants stress level (1-10) is measured pre and post-intervention. They also complete a questionnaire regarding their mental health which ...
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Testing changes in regression predictors between timepoints (independent data) - regression/ANCOVA or mixed model

I have a fairly complex regression model with 14 predictors. I've collected data over five sequential (but not evenly spaced) timepoints, and I want to see whether the importance/direction of the ...
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Trying to interpret ANCOVA in R [duplicate]

here's a brief overview of what I'm trying to do. The dataset I have was collected from an experiment that compared 3 conditions (control, group 1 and group 2) on performance. My first task was to ...
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Effects of pretest-posttest vs ANCOVA approach

I'm trying to see if performance on a task differs among conditions A, B and C. Participants completed an easier version of the task on day 1, and a harder version on day 2, when the intervention took ...
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Is pairwise multiple comparisons necessary with t/wilcox tests?

I have two groups, young and old and within each group, I have four brain regions of interest (2 regions * 2 hemispheres). I have run four separate t_tests in R looking at the difference in means, per ...
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How can I run repeated measure ANCOVA in r?

I originally performed 2x2 repeated measure ANOVA using a dataset. There were two independent variables, within factors (foot position and limbs), and the single-leg jump heights were measured. For ...
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Is it okay to use ANCOVA to show something is correlated to A but not to B?

I did a study to look for a neural correlate to a behavioral performance score, say scoreA. scoreA is obtained in a behavioral test. At the same time, scoreB is also obtained, though I don't care ...
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Appropriate regression model for a learning experiment on alpine skiing

We are running a learning experiment with a between-subjects design on alpine skiing: one group training according to an interleaved schedule whereas the other group train according to a blocked ...
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Ancova in R - Why does the addition of a randomly distributed variable (dominant hand) to model make all the interactions non-significant

After reading tens of articles on linear models I'm here with my first ever question, I'm having real trouble with my first ANCOVA model in which I'm trying to see how response time (divided into two ...
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Compare decadal mean growth rates between age classes

I would like to compare rates and trends between different age classes, but am a bit stuck in finding the best way to do that. I have calculated decadal mean growth rates per 50-yr age class of a time ...
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Testing the Homogeneity of Slopes in Repeated measures ANOVA SPSS

I conducted a repeated measures ANOVA in SPSS, using the command Generalised Linear Model > Repeated Measures. I have a within subject factor with two levels (A), a measure (B) and a covariate (C). ...
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Why is ANCOVA not appropriate for modelling post-intervention outcome, controlling for baseline

I was trying to understand the different use-cases for differences-in-differences models vs. ANCOVA (post-period = pre-period + experiment_group), for observational data. I came across the below ...
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How do I control for baseline differences between groups in a multilevel growth curve?

I am analyzing a repeated measures experiment with 3 groups using a multilevel growth curve in SPSS. I have represented my 3 groups with 2 dummy variables (d1 & d2). I have discovered that there ...
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Running ANCOVA with multiple covariates

I'm running an analysis to explore what factors predict adherence to an intervention study involving different types of activity (either learning a language, learning computer skills, handicrafts, ...
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Running ANCOVA with categorical covariates - how to set up dataset?

I am analyzing a dataset in which 80 participants rated 4 products (product A, product B, product C, product D) from -3 to 3 depending on how much they liked the product. Each participant provided ...
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ANCOVA with random effect

I have searched on how to perform a ANCOVA with random effects, but have had no luck finding anything that definitively tells me if that is allowed, and if it is allowed how to do it? Are ANCOVAs with ...
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Best modelling approach to account for covariates (Linear Mixed Models, ANCOVA, or another option)?

I have some electrophysiology data that I am analyzing with SPSS (I know R however as well if that makes things easier). Participants were recruited (healthy controls and patients) to undergo an ...
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Are there problems with using Ordered Quantile (ORQ) normalization for Multivariate Analysis?

This is intended as a general question, as a Google search for -- "Ordered Quantile" "ORQ" normalization "Multivariate Analysis" -- returns nothing. This option is listed ...
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ANCOVA with count Data (GLM, Quasipoisson) and multiple Covariates (R)

at the moment I am working on my Bachelor Thesis and I got a problem in Data Analysis with ANCOVA in R. Unfortunally the experimental Design leads to a small number of samples. I got 12 Days and 3 ...
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ANCOVA or Repeated measures ANOVA or GLMM or GEE

I've got the following problem: background A unwanted species keeps entering the farms. Some farms might be entered more often than others. There are 80 farms in total, subdivided into two groups: ...
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Two-Way ANCOVA: It is necessary to include a non-significant interaction term in the model?

The objective is to test whether the adjusted group means are equal. The question is whether ANCOVA requires the interaction term, for this objective. In all the guides I am reading, after testing for ...
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Seeking Explanation of how this ANCOVA result in R shows the group means are not equal

I am looking for an explanation as to how the ANCOVA results, below, show that the means of the groups defined by IndVar1 and IndVar2 are not equal, after accounting for the covariate, Covar. I think ...
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Example 2.2.2 fromAn Introduction to Generalized Linear Models. Show $Y_{j k}, \bar{Y}_{j}, \hat{\beta}_{j} $ are all independent

This question is related to what I have asked in my previous post: How to derive the covariance matrix between $\bar{y}$ and $\hat{\beta_c}$ where $\hat{\beta_c}$ is the OLS estimator of a linear ...
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How to adress the -0.71 correlation artefact in the pre-post analysis of change from baseline in non-randomized trials?

Let me make some introduction first. It's well known, that in randomized trials, in the pre-post trials, by the formal pharmaceutical regulatory guidelines, both raw post and change scores should be ...
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ANCOVA post vs. pre analysis on a randomized trial - unequal slopes. How to interpret and report the main effect?

Let's assume I have two randomized trials comparing a new treatment to a reference one, illustrated below with 2 different approaches. I will use R notation. ANCOVA: post ~ pre * treatment (we want ...
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1 factor, 1 covariate, single control group. Is ANCOVA possible?

Let's say in our experiment we have three drugs (factor), each in 3 doses (covariate), with a separate group of subjects assigned to every drug-dose combination, and a single control group (no drug). ...
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Can regression to the mean be corrected by linear mixed effects?

I am wondering if regression to the mean can be corrected by using linear mixed effects models in the following case. ...
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Significant covariate interaction in two-way ANCOVA

I am doing a randomised experimental study in which I have two between group factors (let's call them valence of manipulation and type of manipulation). I am measuring my outcome variable before the ...
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How to interpret this prepost ANCOVA test result?

I have a basic pre-post trial design. Two randomized Groups and two tests for each participant in each group one prior to the intervention (here V1) and one post (V2). I am completely new to this and ...
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Appropriate effect size to report for permutation tests (Anova specifically)

Original question, with explanation of outcome and explanatory variables included. Suppose I have a neuroimaging dataset, e.g. diffusion tensor-derived measure for multiple white matter bundles (or ...
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1answer
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What is the best analytic approach for two arm randomized pre-post trial?

Study design is a classic pre-post design: two trt arms (treatment, control). Subjects are randomly assigned into two arms. outcome is continuous and measured at baseline and a follow-up time point (...
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How can I perform a regression analysis for two groups?

I have a problem where I have three groups (responders versus non-responders at baseline, responders versus non-responders at week8, and responders at baseline compared to responders at week8), in ...
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Longitudinal changes: linear mixed effect model Vs linear model using baseline measure as covariate

I am trying to study longitudinal changes in patients for measure 'a'. I have 2 measures of 'a' at baseline ('a_baseline') and ...
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Controlling the influence of variation in a factor

I sampled communities in different habitats along a continental margin. Depth is a strong structuring factor in the ocean. To mitigate or control the influence of the depth factor and in a comparison ...
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How can this model be fit using R's lm function?

I have data that consists of a grouping variable $\tt{grp}$, a predictor $\tt{x}$, and a response $\tt{y}$. There are three groups. I want to fit to this data the model $y = \alpha_i + (\beta + \...

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