# 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.

473 questions
Filter by
Sorted by
Tagged with
12 views

### 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 ...
13 views

### 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: ...
92 views

### 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 ...
47 views

### 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 ...
36 views

### 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 ...
20 views

### 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 ...
9 views

### 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 ...
28 views

### 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). ...
32 views

### 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. ...
23 views

### 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 ...
16 views

### 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 ...
34 views

### 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 ...
54 views

### 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 (...
13 views

### 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 ...
7 views

### 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 ...
9 views

### 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 ...
38 views

18 views

### ANCOVA when response variable is calculated from 2 covariates

I have an experiment in which I apply a treatment (g), and measure variables X and Y; the response variable (density; Z) is simply X/Y. If I wanted to know if X or Y, when shifted under the treatment, ...
24 views

### Test if intercepts in ancova model are significantly different in R

I ran a model explaining the weight of some plant as a function of time and trying to incorporate the treatment effect. weight ~time + treatment The model looks ...
33 views

### MANOVA or repeated measures anova or ANCOVA?

for my thesis I want to compare 3 training groups (2 different types of training and 1 control group) to see the influence on mindfulness-skills and exhaustion level (so 1 IV and 2 DV). All the ...
75 views

### Interrupted Time Series Analyses in R with Type-2 Sum Squares ANCOVA Lagged Dependent Variable model

I have a short times series (less than 100 data points). I wonder how to compare effects of intervention I on values of time series. I prepared model on dataset Nile available in R. Let's assume that ...