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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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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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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Kruskal-Wallis test allowing for one covariate?

As a non-statistician (I am human geographer, interested in health geography), I am trying to solve a problem (using R). Let's say I have a simplified database called df which contain these variables: ...
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Difference between Repeated measures ANOVA, ANCOVA and Linear mixed effects model

What is the best way to analyze these data: Subjects are divided in two "Group" (Treatment A and B). "Weight" is recorded before and 3 months after treatment. Outcome variable: ...
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ANCOVA with Pre and Inter as covariate

I have 3 groups (CTL, Exposure A and Exposure B), an outcome measured at 3 moments (Pre, Inter, Post), and I am interested in comparing the effectiveness of each exposure at short (Inter) and long (...
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Appropriate statistical test to analyze differences in slopes of time series data in R

I have created the following plot based on air quality data over three years of observation, and would like to know if these slopes are different across the two time periods (March-June 2018-2019 ...
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Comparison of values by group with covariance

I have 3 groups of different sample sizes with covariance I need to include. I wish to evaluate the value dependence of the groups compared to group 1 (group 2, group 3 values compared to group 1). I ...
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Nested data and data analysis options

I want to compare patient experience (continuous DV; N = 60) for three different treatment modalities (face to face, phone, chat; between-subjects variable, one measurement). The sessions were run by ...
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Interpreting ANCOVA results

independent variable gender. Gender is a binary column consisting of 0 and 1.From the linear model summary below my observations are: Gender is significant for height dependent variable. Which means ...
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Factor analysis when I have mixture of continuous and dichotomous variables

I am trying to determine if there is a significant difference between two groups for a single continuous variable while accounting for baseline differences in dichotomous variables in each group. To ...
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How do I perform and interpret an Ancova/Poisson Regression, with multiple covariates and possible interactions?

I am researching how recovery time of trees after tropical wildfires differs between South America, Africa and Australia, using R. For this, I am using a Poisson regression. First I checked if there ...
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Two-group “ANCOVA” with Theil-Sen?

("ANCOVA" might typically refer to using at least three groups. In what I do, I am always comparing two groups, and that is what I mean throughout this question.) I know how to do ANCOVA via ...
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If interested in common a trend in multiple groups, can I pool all the data and run a correlation rather than an ANCOVA?

Dear CrossValidated Community, I have three groups, each of which has some biological data I'll call X, and I am interested in whether X is correlated with their treatment response, Y. Thus far, I ...
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How to interpret the interaction term in an ANCOVA model

Just looking for some help on my ANCOVA analysis. My study is basically looking at the difference in variables at 12 weeks in an exercise group and a control group. In figure 1 included as I ...
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Anconva or Anova for multifactor analysis

I have non-normal plankton community data, where rows are sites and columns are species (dependent) and a few factors. I want to check the influence of season on community (dis)similarities but am ...
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Discrepancies in robust ancova calculated in R with the WRS2 package vs by hand

I've conducted a study where participants in 2 groups (Control and Experimental) completed three scales (NJ, A, and D) at two time points (T1 and T2). I'm running ANCOVAs with the T2 responses as my ...
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Why is the Tukey method not appropriate for covariance analysis when estimating treatment effects?

In the book 'Applied Linear Statistical Models' chapter 22 it states that the Tukey method is not appropriate for covariance analysis. The context is in estimation of treatment effects. Instead, when ...
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Interpreting repeated-measures oneway ANCOVA

I have a question on how to run a repeated-measures oneway ANCOVA. I have only one within-subjects factor (time) and I am interested in how a construct changes from T1 to T2. I would also like to add ...

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