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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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Repeated measures analysis of covariance literature

Does anyone have a literature to study about repeated measures ANCOVA? For example, the concept, assumption, and how to calculate manually?
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Overall ANCOVA not significant but post-hoc pairwise comparison are

I have the following problem: I run a ANCOVA with three time-points and 3 covariates; no factors (groups). My overall ANCOVA is not significant. But all my post-hoc (Bonferroni-adjusted) pairwise ...
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Ancova or other test?

I am struggling to select the correct type of test for my data and would like to eventually run it in R. The design is as follows: A treatment vs control group of plants From each plant the following ...
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Logistic regression for experimental inference?

I'm curious if logistic regression is appropriate when the task is inferring a treatment effect on proportions (ex: success rate) when covariates are present and some imbalance across treatment and ...
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Mixed ANCOVA Assumptions

I have a Mixed ANCOVA. my within-subjects factor is Time [Pre- and post-intervention) and my between-subjects factor is Group [4 intervention]). My IVs are group and time. My DV is happiness, which is ...
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Explain ANCOVA to a newbie

I'm currently doing a statistical analysis between the effect of diversity and population density on depression in different counties across the US. I have currently run a two way ANOVA test and I ...
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Observational pre post design and confounder adjustment

I have observational data with baseline, and two follow-up measures with a binary treatment. Dependant variable is questionnaire scale score ***. I am planning on fitting a linear mixed effects model ...
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Difference between an ANCOVA and an ANOVA on residuals that the effects of covariates are already removed

My psychological experiment has a repeated-measures design. Each participant performed 4 conditions (Factor A [2 levels] X Factor B [2 levels]). Let say the DV is the accuracy of the participants and ...
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Mixed Effects with repeated measures design and covariate included

I have a dataset that consists of the oxygen consumption (MO2) values for 3 different species of fish. My experiment was a repeated measures design where I measured MO2 of the same 14 fish per species ...
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1 answer
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Power analysis for ANCOVA

I'm interested in conducting power analysis for experiment design and inference using ANCOVA. I see questions A,B,C vary in terms of quality, applicably and answers; whereas I'm interested in an ...
jbuddy_13's user avatar
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Can you assess Moderation with ANCOVA?

I am using SPSS for analysis with 1 group IV (4 levels), one DV measured at time 1 and time 2 for each participant in each group, and one covariate measured once at time 2 or for each participant in ...
Johnny A's user avatar
2 votes
2 answers
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ANCOVA or MODERATION?

I'm struggling with the statistics for a question I'm collecting data to answer. My paper is about whether different meditation types can increase happiness when controlling for meaning in life. There ...
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ANCOVA main ideas [duplicate]

Is Analysis of Covariance just OLS regression plus a hypothesis test on top of predicted y-values? $\hat{y} = BX = B_{treatment}treatment + X_{2...n}B_{2...n}+B_0$ $H_0: \mu_{\hat{y}_{treatment}} - \...
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In a 2 arm pre-post RCT, is an interaction test on an ANOVA the same as a t-test of the change scores?

Say you have a 2-armed pre-test post-test control trial design. You want to test the effect of group allocation on the outcome variable. I simulated a version of this in R, using 3 different methods: ...
Joel Phillips's user avatar
8 votes
3 answers
521 views

Comparison of 2 groups with covariate

I compared 2 groups and found that their test scores are significantly different. However, I also found that they are significantly different in the mean age. I want to see if the scores between the ...
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Repeated measure (2 situations) with skewed data and a covariate

I made repeated measure of all participants in 2 situations (situation A and B) for devaluing comments (devComnts) as outcome (measured as proportion: devaluing comments / all comments). Distributions ...
Pernille's user avatar
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Non-parametric ANCOVA post hoc test

I am doing a non-parametric ANCOVA (my residuals are not normally distributed and transformation did not help), I have been using the sm.ancova function from the sm package in R. Now I want to do a ...
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Got a constructed (sum of items) ordinal IV for a Factorial ANCOVA , how to treat covariates?

I will measure an independent variable (IV) using a 5-point Likert scale on 5 attitude objects. Now, I want to create an IV where the levels represent the occurrences where the participant has a score ...
GT87's user avatar
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Is Type III ANCOVA warranted?

I'm running the following ANCOVA: m1 <- aov(formula = Rate ~ Treatment * Species * Weight, data = Data) car::ANOVA(m1, type = 2) My design is a bit unbalanced ...
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DiD vs Repeated meausres ANOVA vs ANCOVA

I am learning statistical analyses for experimental and quasi-experimental studies. From my class and by searching answers here and asking ChatGPT, I have some preliminary understandings of Difference-...
Jack Learning stats's user avatar
1 vote
1 answer
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Paired t-test or ANCOVA or linear mixed model?

Recently I encountered a situation where each subject has a continuous response variable at 3 time points ($t_0$, $t_1$, $t_2$). There are $3$ treatment groups ($A,B,C$), and some covariates. Consider ...
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Can I 'double' dip into a baseline to both reduce variance, and use it as a level of my with factor of time?

I have a bit of a situation I would like some advice on. I'm currently running a human subjects study where I have two groups (group 1 and group 2), and three time points. Each subject performs a ...
JBugg's user avatar
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2 votes
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ANCOVA sensitivity to large variation existing in only one of the groups

I plan to run ANCOVA to test the effect of diet intervention across 3 groups. I have before and after intervention measurements and use before measurements as covariate ( ...
user407145's user avatar
4 votes
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Nonlinear relation between two variables as affected by two interacting treatments

I experimentally tested the relation between dependent variable y (continuous) and independent variable x (continuous) for 6 replicates x 2 genotypes (categorical) x 3 species (categorical) each (= ...
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1 answer
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ANOVA, ANCOVA, linear mixed effect model

I experimentally tested the relation between dependent variable $y$ (continuous) and independent variable $x$ (continuous) for $10$ replicates of $2$ plant varieties (categorical) of $3$ species (...
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How do I calculate effect size in a pretest-posttest three group randomized study for two planned contrasts (ANCOVA)?

I am having a hard time calculating the individual effect sizes for ANCOVA simple contrasts ($1$ vs. $2$ and $1$ vs. $3$) in a randomized pretest-posttest design study with three groups. In the ANCOVA,...
Eniko's user avatar
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1 vote
1 answer
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Which test should be used for an ordinal dependent variable with pretest-posttest and two factors?

Consider a pretest-posttest design, where the dependent variable (y) is measured by 3 ordinal values 1,2,3. There are also two factors: One factor (say A) consists of a control and an experimental ...
M. Er's user avatar
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2 votes
1 answer
82 views

Is Multiple Comparison Correction necessary for multiple ANCOVA tests

I'm working on fMRI data comparing brain activation from ten different brain areas across three groups after controlling for covariates such as age, sex, disease severity. I built an ANCOVA model with ...
SStt1002's user avatar
2 votes
1 answer
99 views

Power analysis for a quasi-experimental factorial design 3(manipulated) x 1 (measured) ANCOVA

I'm experiencing an hard time looking for the proper analysis to use to compute the power for an experiment i'd like to implement, so here is my question for you. I'd like to run a quasi-experimental ...
GT87's user avatar
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1 vote
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How can I compare the results of two lmRob() models? [closed]

I am looking for a way to compare the results from two lmRob() functions statistically. Would that be a possible option for me: lmrob_female <- robust::lmRob(Y ~ X_binary + covariate1 + covariate2 +...
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Doubt on non-parametric ANCOVA with two groups and pre-post scores and pre scores (baseline) as covariate

I have used a non parametric ANCOVA to analyze scores of a questionnaire (BSCS) with factors: Type of intervention(A and B) and timepoint (pre- and post) as well as baseline (same distribution as pre-)...
Fil's user avatar
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How to get an overall P-value for a categorical variable, If I know the t-values of its dummy variables?

I am doing ANCOVA: main categorical variable for the comparison is "Street" and it contains 3 categories (Street1, Street2 and Street3). The outcome variable is social interaction time (...
Hussain's user avatar
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1 answer
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ANOVA/ANCOVA results in SPSS

I am unsure about how to interpret the output box I get doing an ANOVA in SPSS. That's the "Tests of between-subject effects" box in particular. I had 2 groups (A and B), and 2 results (...
Rene's user avatar
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Repeated Measures ANOVA with two covariates

I am doing a repeated measures Anova My variables are like this: Y - continues variable measured pre and post intervention Intervention - the between group variable with three levels in which ...
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Statistical analysis on cortisol reactivity (longitudinal)

I collected stress data (cortisol reactivity) on 4 timepoints. I also collected psychological measures at 1 timepoint. I would like to know if the psychological measure (one measurement time point) is ...
Michi19's user avatar
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Homogeneity of regression slopes and collinearly of covariates in ANCOVA (specific)

Thank you for such a great website for statistics learners, I am currently studying a factorial ANCOVA and have two questions: do we need to test homogeneity of regression slopes for an interaction ...
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Repeated Measures Ancova In R

I apologize if I am not being very clear, I have basic knowledge in statistics! I am trying to analyse my data but I am unsure if repeated measures ancova is the way to go. I have a variable named &...
Aron Golding's user avatar
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1 answer
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Repeated measures Ancova in R

I am trying to analyse my data but I am unsure if repeated measures ancova is the way to go. I have a variable named "A" measured in three different conditions "1", "2" ...
Aron Golding's user avatar
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1 answer
683 views

How to calculate slope and linear regression in R

After creating the plot using: ...
user400341's user avatar
1 vote
1 answer
19 views

Can I add more than 2 independent groups to an Ancova and if so, do I need to create dummy variables in SPSS

I want to analyze the difference between 4 groups on one dependent variable while controlling for my covariate, age, and 3 different independent variables (sex, cancer type, metastasis) in SPSS. Can I ...
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Interpretation of ANCOVA output

I am struggling to interpret my ANCOVA output - I have looked at similar questions and can't figure it out. I am looking to determine whether there are gender differences in the impact of a specified ...
bsh7194's user avatar
3 votes
1 answer
165 views

ANCOVA in within-subject design

I have two questions regarding an ANCOVA analysis in SPSS in a within-subject (i.e., repeated measures) design (e.g., an experiment with 3 measurement timepoints): when checking ANCOVA assumptions, ...
Manuel Leitner's user avatar
1 vote
1 answer
47 views

Doubt on checking linearity assumption in a mixed-ANCOVA design

I am a PhD student and I have to run a mixed-ANCOVA on some questionnaire scores (my dependent variable) according to the following model. Factors of ANCOVA are (a) Timepoint (pre-intervention, post-...
Fil's user avatar
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1 answer
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Normalised versus true racing times as DV for a learning experiment?

I have a question about using ratios as variables in alpine ski racing research. We want to compare skiers' performance on different days, but snow conditions affect the results. To address this, we ...
Cmagelssen's user avatar
1 vote
1 answer
125 views

How to analyze nested data of repeated measurements? ANCOVA or linear mixed model?

I have obtained a dataset from a psychological experiment. In the experiment, each subject completed four sessions of tasks on four different days. Each session consisted of two stages of tasks. ...
Steven C's user avatar
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1 answer
71 views

How should I proceed with a one-way ANOVA if homogeneity of variance is violated, I have unequal sample sizes, and I want to control for covariates?

I'm using SPSS. I have a multi-level categorical IV and a few continuous DV's. My main analysis goals are to test the effect of the IV on the DV, and then to follow-up with pairwise comparisons of ...
Joanna Demaree-Cotton's user avatar
1 vote
1 answer
71 views

What to do after violation of homogeneity of regression in ANCOVA

I wanted to run an ANCOVA. My independent variable is field of study (3 groups: science, humanities, and business). My dependent variable is IQ measured on a continuous scale. There are two covariates:...
FastBallooningHead's user avatar
1 vote
0 answers
279 views

How to properly include covariates in a one-way repeated measures ANCOVA? What do results tell me?

I want to test the effect of a suicide prevention film on help-seeking. I have help-seeking intentions as an outcome variable and measured this variable at three time points (pre, post, follow-up) in ...
Gabriel Dobroschke's user avatar
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0 answers
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An ANCOVA pre-post framework for multilevel data?

I have a continuous outcome/dependent variable that is measured multiple times before and after an treatment/intervention per subject. The multiple measures are performed very closely together and are ...
RmyjuloR's user avatar
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1 vote
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What statistical test should be used for pre/post data (that violate ANCOVA assumptions)?

I want to assess the effect of a treatment (control vs. ash) on a continuous variable (e.g. calcium concentrations). I have two additional grouping variables that are also both categorical: location (...
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