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.

5
votes
1answer
19 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
18 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
8 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. This is pretty ...
2
votes
1answer
31 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
14 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
10 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
17 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
12 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
19 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
21 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
22 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
14 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
11 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 ...
2
votes
1answer
75 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
46 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
42 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
15 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
34 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
17 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
15 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
25 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
11 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
33 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
31 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
21 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
30 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
65 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
18 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
50 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
70 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 ...
1
vote
0answers
26 views

What to do when there is heteroskedasticity in an ANCOVA model?

What to do when there is heteroskedasticity in an ANCOVA model? Is there a correction similar to Welch ANOVA? Or is better to use a OLS regression model? Should we try to solve heteroskedasticity by ...
1
vote
0answers
18 views

Is ANCOVA suitable/scientifically sound for my case?

I have a question regarding the suitability of co-variate. I have three groups with different levels of production in pcs (low, medium, high), material waste in % and number of machine setup changes. ...
0
votes
1answer
27 views

How to calcualte confidence interval for the residual variance in ANCOVA models

As the question states I need to know how to calculate this. Given variable $Y$ and $X$ with $\operatorname{cor}(Y,x)=r$, the residual variance is: $$(1-r^2)\cdot\sigma_Y^2,$$ which represents the ...
1
vote
1answer
33 views

merit of t-test vs repeated measures

In a cohort study, patients have been enrolled for a new method of treatment of a condition. The measurement of interest, for example, tumour size is taken at baseline (BL) ie before treatment, the ...
2
votes
1answer
44 views

Interaction in ANCOVA

I'm doing a study with frogs in which I see that there are differences in jumping ability between juveniles and adults, I get that adults jump more than juveniles. I want to check if these ...
1
vote
0answers
33 views

Statistical analysis techniques for pre and post repeated measures

I am trying to understand which is the appropriate statistical technique to use for the below experimental design: Design: I have two groups - an intervention group (that took an action, eg increased ...
0
votes
1answer
30 views

Comparing the results of 2 different type but identical samples from 2 devices

I have 2 columns of of the concentration of fat in fish which is measured by 2 different labs. I need to know if the difference of the results from these 2 labs are statistically significant. The data ...
0
votes
0answers
24 views

ANCOVA multiple confounding continuous variables

I want to perform an ANCOVA analysis to test whether mpg shows differences between a categorical variable am; together I want ...
1
vote
2answers
52 views

Significant main effects lost during ANCOVA due to interaction terms. Is type III the way to go?

I have some experimental data which I am analysing using step wise multiple regression (ANCOVA) in R using the step function. The response data (wp) is the leaf ...
1
vote
0answers
20 views

Interaction between covariate and 2-level within-subjects factor is of research interest. How to test

I'm interested in interpreting the interaction between a continuous variable (C) with a dichotomous within-persons factor (A) on a continuous DV (DV). What is the best overall test of this? Would it ...
1
vote
1answer
21 views

Can I do it through Repeated Measures ANCOVA? If so, how can I interpret the results?

I'd like to have some help, please. I'm writing my masters and I have a huge doubt about which test should I use. What I want to measure is: the effect of therapy on people who have and don't have ...
0
votes
0answers
36 views

What statistical tests should I use for this between-subject user study?

So, I have performed a between subject experiment, where half of the users used Tool A to perform the Task and the other half used Tool B to perform the Task. Each tool had specific mechanics to ...
1
vote
0answers
47 views

ANCOVA - Non-linearity of covariate

I have a dataset where I calculated genetic distances between populations of some animals (a continuous variable). I want to know if these differences are explained by physical or/and ecological ...
0
votes
1answer
97 views

How do I perform an ANCOVA ? (master thesis deadline) [closed]

My dataset consists of several morphological measurements for 5 island populations of a certain lizard species. I want to test for each population if there is a significant difference in the ...
0
votes
1answer
122 views

Covariates and moderator variables

I have a 4 * 3 (both the IVs are categorical) factorial design with two covariates (both are continuous) to run ANCOVA. Can I do a moderation analysis?
0
votes
0answers
30 views

Time series regression

I have a dataset of SO4 concentration (annually) from 1986-2016 across 35 water catchment stations. The dataset looks like this: I first plotted the data and found out that the trend pattern is ...
0
votes
1answer
99 views

Further analysis of significant interaction between a covariate and independent variable

I am studying to see if there are differences in mussel feeding ability (CR) based on 10 different food types (Taxa) and water source (Treatment) using the covariates shell length (SL) and Initial ...
0
votes
1answer
46 views

Comparing Multi-Year Survey Data (Is Repeated Measures ANOVA appropriate?)

I have a question which requires your helpful expertise. I am conducting a survey which, through the utilization of a scaled response from participants (1-10), measures for significance in ...