Stack Exchange Network

Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

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.

0
votes
0answers
14 views

Getting marginal means for ANCOVA in R (effect vs emmeans)

I'm a bit new to running GLM models in R, so forgive me is this is a silly question. Context: I'm running an ANCOVA with the goal to control for multiple covariates while understanding the ...
4
votes
1answer
35 views

3x2 within subjects design with covariate that is nested within factor (?)

I want to test the differences in my interval-scaled dependent variable - measured at three time intervals (within subj.), for two conditions (within subj.), while accounting for a interval-scaled ...
0
votes
0answers
14 views

ANCOVA: resolving hetrogeneity of regression slopes with multilevel modelling vs adding an interaction term

On the Wikipedia page for Multilevel model it is written that [M]ultilevel models can be used as an alternative to ANCOVA, where scores on the dependent variable are adjusted for covariates (e.g....
1
vote
1answer
35 views

Does it make sense to do Levene's test in relation to ANCOVA?

In relation to another question, Ben Bolker writes that if you have all-categorical predictors, you can test for heteroscedasticity (and other issues such as non-Normality) by dividing the ...
2
votes
0answers
48 views

Using a t-test to follow-up on a non-significant interaction in an ANCOVA?

My question is about whether a t-test can be used to follow-up on a non-significant interaction found with an ANCOVA. I have an experiment that compares the impacts on students' learning (as measured ...
0
votes
0answers
7 views

Negative coefficient in model caused by weak multicollinearity

I performed multiple regression and obtained the following model: Q = (0.33495)P + (-76.89321)G + (6.31424)P・G - 3.36334 P = precipitation; G = groundwater; Q = stream discharge The coefficient of (...
0
votes
0answers
22 views

Adding covariate to GLM

My response variable is a count data (vse23). My explanatory variables are a combination of continuous (zastska, razkrit, zastveg) and categorical factors (mezo). I did a GLM model of variables that ...
0
votes
0answers
2 views

What does it mean when running ANCOVA with two moderators and one of the interactions is insignificant when ran together?

I am hypothesizing that there are two moderators in the relationship between IV and DV. I ran one ANCOVA with moderator A and the interaction between IV and moderator A is significant. Then I ran ...
0
votes
0answers
9 views

Control for two variables in repeated measure ANOVA

I have a 2 factors repeated measure ANOVA for measuring Response Time to stimuli in two different contexts with two different stimulus types. The context and is not supposed to have any main effect. ...
0
votes
1answer
31 views

Am I Log Normalizing correctly?

I am sorry if this is a stupid question, but I have searched the other questions about log normalization found other sources on it all of which assume a level of understanding that I don't have. I ...
0
votes
0answers
18 views

How do I conduct an ANCOVA within a pre and posttest design?

I have a question regarding the analysis of my quasi field experiment. I conducted an experiment in a high school where a class learns over 5 weeks with a smart personal assistant (n=22) and the other ...
1
vote
1answer
33 views

figuring out ANCOVA in R [closed]

I am not too familiar with using R for stats, but I really need to be able to analyze my data. I am comparing the level of a compound found in plants from two different locations, and within each ...
0
votes
0answers
10 views

Should I report the mean value of a DV before or after partialling out covariates?

I have the results of some ANCOVAS with 4 covariates. The mean value of the DV before and after partialling out the covariates is very different. Would you report both Mean values or just the one ...
0
votes
1answer
18 views

ANCOVA with Polynomial Categorical Variable

I have a homework problem that asks me to fit a one way ANCOVA model to a set of data (which I feel comfortable with). The model is represented as yij = μi + γzij + eij where i indicates ...
0
votes
1answer
10 views

How to transform a continuous variable which is a moderator in ANCOVA into a categorical one?

How do I decide where is the threshold to split it into levels? I ran an ANCOVA with a continuous moderator and it is significant, but I am wondering how to transform it to a categorical variable? Is ...
0
votes
0answers
12 views

Difference between MANCOVA and multiple ANCOVAs

I am analyzing the volumes of 13 different regions in the brain in a longitudinal (baseline and followup) study. I have two groups of participants - the therapy group and control group, and two time ...
0
votes
0answers
21 views

SPSS ANCOVA interaction significant once main effects removed

I'm running a 2x2 factorial ANCOVA, where the factors are either being in condition A or B and either being part of a certain group or not, with two covariates being age and gender. When I run the ...
0
votes
0answers
14 views

Within Correlation with ANCOVA or Multiple Regression

i have recently tried to understand a measure for within correlation from the paper (Bland & Altmann, 1995): https://www.bmj.com/content/310/6977/446.full The trouble is, the paper describes ...
5
votes
1answer
41 views

Pairwise comparisons of regression coefficients [duplicate]

I would like to know how to make quickly pairwise comparisons of regressions coefficients across three or more groups in R. Here is a small example: ...
0
votes
0answers
24 views

If change is DV and Pretest is covariate, should random effects take the form of (1|subjects) or (Pretest|subjects)?

I have Change from Pretest to Posttest (gain, no_gain, decline) as the DV. Pretest and Group as covariates. This called for a multinomial regression ...
0
votes
0answers
15 views

Account for covariate after predictor in ANCOVA?

I've been thinking about ANCOVA a bit and I didn't find anything on this particular issue. One of the most critical assumptions is that the predictor is not correlated with covariate (assumption of ...
2
votes
1answer
32 views

ANOVA OR ANCOVA?

I have 3 different groups of people that completed a language task. Some individuals took a drug and some did not. I would like to investigate the effect of the drug on performance in the different ...
0
votes
0answers
20 views

Ancova for unequal variances [duplicate]

What is the best way to compare two non-homogeinous populations (Levene's) with covariates (e.g. age). I know ancova assumes homogeneity. Is there a way around this? Many thanks
0
votes
0answers
18 views

How to calculte sample size of Mixed ANCOVA(2x2x2) using G*power

I want to know how to calculate the sample size of a Mixed ANCOVA model using the G*Power software. The study design is 2(between)x2(with-in)x2(between) and there ...
0
votes
0answers
19 views

Interaction not significant anymore in ANCOVA, but in ANOVA

I have a significant interaction $A\times B$ in my regular mixed ANOVA, but when I add a covariate, the effect $A\times B$ is no longer significant, but the interaction effect with the covariate $A\...
0
votes
0answers
27 views

Grouped data as independent variable for continuous outcome

I have an independent variable grouped into irregularly sized classes (0, 1-5, 6-10, 11-20, >20), a continuous dependent variable, and several control variables. So far I've been trying to stay close ...
0
votes
0answers
36 views

SPSS ANCOVA with robust standard errors estimates

I am using SPSS version 25 to run an ANCOVA with heteroskedastic-consistent standard errors estimators (HC3 procedure) and I am puzzled by some of the output I get. I am fine with the robust standard ...
0
votes
1answer
60 views

Two-way ANCOVA with a between-subject variable in R

I have a dataset with a 2x2x2 design: Group (CTL vs. SC) x Session (Sess 1 vs. Sess 2) x Treatment (Treat vs. Placebo). The dependent variable is Response Time. I also have a variable Age. I would ...
1
vote
1answer
29 views

Steps to conduct ANCOVA between two groups that has 2 covariate?

Using R, I want to compare two groups (1 & 2), each group having two covariate. More specifically, i need to: Within each group, test for significant relationships between the dependent variable (...
0
votes
0answers
33 views

Bootstrapping ANCOVA to deal with violations of assumptions

I have a smallish data set with three randomised intervention groups ($n$s between 13 and 22), with pre-post variables. I want to run an ANCOVA with the pre-data as a covariate and post as an outcome ...
1
vote
0answers
12 views

Can ANCOVA be used for the following model

Suppose I have 3 treatment groups, and I have pre- and post-treatment test results. There are also 4 covariates which theoreticlaly can influence the post-outcome. So is it possible to find which ...
3
votes
1answer
165 views

Why is my Mixed Effects Model (LME) results different from my repeated measures ANCOVA (AOV) results?

I have been trying to compare the effect of a treatment over time, controlling for a continuous covariate. So two groups (treatment vs control) are given different treatments and compared pre and post....
3
votes
0answers
22 views

Compare slopes between two groups of equal size

I want to compare how does a dependent variable (total flow) changes with a covariate (total rain) between two groups (stream A & B). Usually, i would go with ANCOVA. But these groups have the ...
2
votes
1answer
52 views

Ancova: How to proceed when residuals are not normal distrubuted but transformation changes meaning of results

I am trying to analyze water nutrient (DIN) at three different sites along distance transects perpendicular to the coast. The transects were sampled in two years (year t1 and t2) in two seasons (1 ...
0
votes
1answer
43 views

Slope is negative but confidence limits contain zero, how do I describe the effect?

I performed an ANCOVA on final height (height4) with initial height as a covariate. Dependent variables: ipc.gm = initial % cover of garlic mustard fence = factor with 2 levels: Fence, Open There ...
1
vote
0answers
25 views

Dummy Coding ANCOVA in spss [closed]

Scenario: 1 continuous DV = problem solving ability 1 categorical IV = exposure, no exposure 1 categorical covariate = previous preference (like, dislike, neutral) How do I dummy code the covariate ...
0
votes
0answers
63 views

ANCOVA significant interactions in R: How do I interpret slopes from interaction plots?

I've got a continuous dependent variable height4, a continuous covariate height, a continuous dependent variable ipc.gm, and a factor fence with 2 levels: Fence and Open. I've got a significant ...
0
votes
0answers
24 views

When to include covariates when I hypothesize there's a difference between groups?

If I am hypothesizing that there is gender difference in a certain domain, and that another variable would moderate the gender difference, should I include covariates in the analysis? The key of this ...
1
vote
0answers
25 views

p-value of Covariate differs between Regression and ANCOVA

I'm using SPSS to run a regression analysis in order to predict navigational performance (continuous dependent variable) from self-assessment scores (continuous predictor), sex and age group (both ...
0
votes
0answers
52 views

Centering covariates with repeated measures ANCOVA

I have a study design with a repeated measures variable (four time points) and a time-invariant covariate. I am analyzing the data using a repeated measures ANCOVA in SPSS. I am interested in the ...
0
votes
0answers
15 views

Valid use of repeated measures ANCOVA

I am running a repeated measures study with four time points. A single group of participants receive the same questionnaire at each time point, which is assessing variable X. I am determining how ...
0
votes
0answers
34 views

How to statistically compare feature sets with different levels of data collapsing over category and training splits?

Background: As part of my research into image classification from small numbers of examples: I created 4 disjoint feature sets by extracting activations from different layers of a deep neural network ...
0
votes
1answer
33 views

Test to compare on an ordinal scale, two groups of data that have covariates

I have two (Test and Control) groups of data. Data in each group is divided into 10 (ordinal) period. In each of these periods, number of observation ranges anywhere from 22-53. The assumption is that ...
0
votes
0answers
27 views

Step-wise Multiple Regression or ANCOVA

I have an assignment that gives a dataset and a choice of 3 tests: Step-wise Multiple Regression, ANCOVA and Log-Linear Analysis. The dataset consists of ...
0
votes
1answer
47 views

Hypotheses check with mixed ANOVA, ANCOVA, regression or multilevel linear model?

I conducted a repeated-measures experiment and obtained for each subject the following data: ...
0
votes
1answer
137 views

What post-hoc analysis should I use following a two-way ANCOVA with factor, integer and numeric variables?

I ran a two-way ANCOVA on the data below, in r-studio, to determine whether pupal weights Pupal.wt were affected by caterpillars' diet ...
0
votes
0answers
11 views

Trying to find whether a categorical (gender) and numeric variable (heart rate) differ between each other while controlling for Age

so I tried to use ANCOVA in R and when I was doing the diagnostics test, turns out the data is not normalized. Now I am stuck, and I do not know where to go from here. Please help. Is there a way that ...
0
votes
0answers
19 views

ANCOVA vs Random effect for category

Assuming a categorical variable is a nuisance variable, why would one ever use it as a fixed effect as in ANCOVA instead of using it as a random effect? As an example consider modeling the ...
0
votes
0answers
79 views

GPower Sample Size Error with Large ANCOVA Model

I am trying to do a power calculation that with a very large ANCOVA model but am getting an error because my number of groups is too large. I have 14 binary variables, two 4 factor variables, a 5 ...
0
votes
1answer
146 views

Two Way ANOVA or ANCOVA?

I have three groups, one control, one having high fat diet and one having high fat diet+treatment and i want to measure the concentration of glucose over a period of time in these groups. Should I use ...