Analysis of Covariance.

learn more… | top users | synonyms

1
vote
1answer
16 views

Ancova Levene's test significant

I did ANCOVA with Depended: Posttest/ Fixed: Group/ Covariate: pretest Levene's test is statistically significant: .002 Is the assumption of homogeneity of variance violated? If yes , what can i do ...
0
votes
0answers
5 views

Repeated measures ANCOVA - heterogeneity of slopes

In my 2x2x2 mixed model ANCOVA, the covariate is interacting with only one of the main effects (repeated measures). Would it be OK to interpret the rest of the effects and interactions (which were not ...
0
votes
0answers
21 views

ANCOVA; CIs for the intercepts of each treatment

I am currently doing an ANCOVA, and I need to calculate CIs for the intercepts of each treatment (categorical) group. So, instead of using lm(y~x+group), which gives me SEs of treatment contrasts, I ...
1
vote
0answers
18 views

I want to compare two calibrations with R… But cannot find the right answer

I first want to precise that I spent 2 hours searching for an answer, couldn't find something that was answering my question. So basically, I ran two calibration with my diagnostic test, so I ...
0
votes
1answer
15 views

interpretation baseline corrected ANCOVA

I hope you can help me with some statistic 'problem', or maybe check is more accurate =]. I have data on an experiment with a 2 by 3 design, with session(first/second) and medication(a/b/c) as ...
0
votes
0answers
15 views

Is it necessary for covariates in an ANCOVA model to be normally distributed? [duplicate]

I am running an ANCOVA model and am trying to remain true to all the statistical assumptions. I noticed that one of my covariates is not normally distributed, I know that the X and Y variables should ...
1
vote
1answer
26 views

Using ANCOVA when the covariate is not normally distributed

I have conducted a repeated-measures ANOVA, but a reviewer suspects that the observed main effect of condition are due to a the difference between hit rates of two conditions (one of them is ...
0
votes
0answers
18 views

Nonlinear form of ANCOVA?

I would like to compare a control group against a test group using something like ANCOVA. However, the covariates are not simple, as some items may have already been increasing with time, others ...
1
vote
0answers
22 views

Running 2x2x2 ANCOVA in SPSS

I need to conduct an ANCOVA on my data. While I've taken a number of statistics courses, I have never come across ANCOVAs and I want to get some feedback on the correct way to conduct this analysis. ...
0
votes
0answers
6 views

how to analyse an interaction in a within-subjects repeated ANCOVA post-hoc?

I have pre and post measures of attention that I am examining in a within-subjects repeated measures design. I wanted to check the effect of verbal intelligence [VIQ] on my attention[pre/post] ...
0
votes
1answer
21 views

What can be done when a covariate was influenced by the experimental treatment?

I have a problem regarding my data for an ANCOVA. I conducted an experiment with a 2x2 between subjects design (4 different treatment groups) and covariates. Due to the treatment I was just able to ...
2
votes
2answers
51 views

When to create a control group with paired T test

So if I wanted to measure the effect of a drug on a group of people, I think I would use a paired T test based on my research. But what if something caused a change in my group that I did not account ...
1
vote
0answers
10 views

Multiple Ancova's and adjustments to p-values

I am running about 10 Ancova's and am unsure about whether I adjust the overall p-value and then also the posthoc analyses p values. If the categorical independent factor has 3 or more levels. do I ...
0
votes
0answers
15 views

Compare multiple linear regression lines

I am comparing three regression lines (three spp). I could compared spp1 to spp 2 and spp3 but I couldn't compare spp2 to spp 3. Can anyone help on this? Thanks ...
0
votes
0answers
19 views

Repeat measures regress

I have a question about using regression for repeat measures analysis. I have a design in which each participant viewed 4 sets of pictures. 2 sets were positive and 2 were negative. There were 2 ...
3
votes
0answers
99 views

Report in ANCOVA: descriptive means or estimated marginal means?

I have conducted an analysis of covariance, ANCOVA, followed by Bonferroni post-hoc tests, on SPSS. I want to report the differences between my groups in text (APA style) and in a corresponding bar ...
2
votes
2answers
80 views

Between-subjects effect becomes non-signicant after centering covariate. Should I center or not?

I've used a general linear model function to run an ANCOVA, involving a categorical predictor (with two levels), a continuous predictor, and their interaction effect. If I don't center the ...
0
votes
0answers
20 views

Studying pre- and post-treatment change of mean score of a population

I am doing a research studying if a diabetic drug would improve patient's diabetic control. In this study I would enroll a few hundred patients with diabetes. Diabetic control will be measure by the ...
0
votes
0answers
20 views

When to plot different slopes for different treatments in ANCOVA

I am running an ANCOVA with a treatment of 3 levels and a continuous co-variate. Using step() in r, the simplest model includes the treatment factor and the co-variate, but not their interaction. To ...
1
vote
0answers
16 views

error variance in ANCOVA vs ANOVA

If for both the treatment and control groups the correlation between the covariate x and the dependent variable y is substantial but negative, the error variance for ANCOVA as compared to ANOVA (less, ...
0
votes
0answers
21 views

split plot with continuous sub-plot factor?

Question in a nutshell: In a split-plot design, can factor B, the treatment applied to the subplot, be a continuous variable, and can there only be one block?(I read that blocks in split-plot designs ...
2
votes
1answer
21 views

Covariate related to independent variable - best solutions

I have 2 groups (tinnitus sufferers and controls) who are significantly different in age - I would normally control for age as a covariate (as it is a cognitive task) but it violates the assumption of ...
1
vote
1answer
76 views

Permutation on multiple Pairwise Comparison with least square means in R 3.1.2

I'm working on a study where I employed an analysis of covariance (Ancova) with unbalanced factors. I used permutation tests to obtain p-values for my estimates since my observation does not come from ...
0
votes
0answers
12 views

How to calculate y predictor based on ANCOVA estimates? [duplicate]

My formula looks like this: lm(formula=BearWeight ~ honey + age, data=BearData) my output looks like this I am told to interpret each estimate and then use the estimates to predict the weight of a ...
3
votes
0answers
61 views

Regression using aggregate (averaged) data

I'm doing a project involving the impact that different college grading systems have on MCAT performance. I have access to the following data: Grading system by college Median MCAT score by college ...
0
votes
0answers
17 views

Adjusting for Baseline values

In a RCT setting where we have 1 treatment group vs 1 placebo, we want to investigate the effects of the active treatment to a particular lab result. If we have the results for the baseline lab exam ...
0
votes
1answer
30 views

Reporting results of a Quade test

I have been scouring the internet to find out how to report the results of a Quade test (non-parametric equivalent of ANCOVA). Does someone have an example that explains this in plain terms? I'm not ...
0
votes
1answer
27 views

Pretest-Posttest comparison

I am having a hard time doing this on Stata. I have a group of 32 students. All perform a pretest and are scored. Next, half of them are randomized to receiving an intervention and the other half ...
0
votes
1answer
12 views

Can ANCOVA be used to control for lengths of treatment?

I have the same treatment I administered to two groups (experimentals and controls). (This is a hypothetical study asked by one of my students.) The experimental group received the treatment for 6 ...
2
votes
1answer
97 views

Statistical test for repeated measures ANOVA with covariates

We have 10 participants who have undergone a cold pressor test (for pain) in 3 conditions (no drug, drug A, drug B). It is a repeated measure design. The stimulus is continued for 1 minute after they ...
0
votes
1answer
65 views

Calcuate Bayes Factor for Adjusted Mean Difference

I have an ANCOVA model shown below (fit) where I calculated the mean difference between two groups while controlling for another variable (x). For the adjusted mean difference (288.72), I'd like to ...
0
votes
0answers
69 views

time-varying covariates in ANCOVA

I have a problem for which I can't find definite answer so I'll post the question here and hope that someone will be able to help! as it may be clear from the title, I am planing to analyze my data ...
1
vote
1answer
23 views

Correlation between dependent variable and the covariate in an ANCOVA

I want to check the effect that a categorical between-subjects factor A and a continuous predictor B has on a certain dep. variable. I created an ANCOVA with A as a factor and B as a covariate. This ...
0
votes
0answers
68 views

How to write the null hypothesis for ANCOVA

I want to write the null hypothesis for ANCOVA. I have a dependent variable which is scale data (posttest) and the independent variable is teaching method with four categorical levels. The covariate ...
0
votes
1answer
11 views

confound significantly different across groups

I feel this has to come up quite frequently, but there seems to be little clarity in how to handle the problem. If you have a demographic variable (e.g. age, edu) that significantly differs across ...
0
votes
0answers
14 views

ANCOVA: what do I do when my covariate and DV do not correlate?

I was planning to use an ANCOVA for my study, however, the CV and DV do not correlate. In this case can I instead use an ANOVA?
0
votes
0answers
35 views

Proper “normalization” of post-test data to pre-test conditions

I'm performing an in vitro assay in which cells are treated with different combinations of two different compounds and the activity of the cells following treatment is measured. There are 3 ...
0
votes
0answers
26 views

Two way ANOVA or ANCOVA

I need to show that BMI of adults is neither age nor gender specific. Should I do ANCOVA or randomly make age groups and do two way ANOVA?
1
vote
0answers
68 views

How do I test for homogeneity of regression in MANCOVA?

I am using a one-way independent MANCOVA with 4 dependent variables and a single covariate. My predictor is bivariate. I'm currently trying to test for heterogeneity of regression in SPSS by ...
0
votes
0answers
45 views

R - Robust Ancova: Documentation/Examples for the ancmg function in the WRS package

Could anyone point me to a documentation or even better an example for the ancmg1 or ancmg functions of the WRS-package. There is a very short paragraph in the Wilcox' book about Robust Estimation, ...
17
votes
4answers
334 views

Good data example needed with covariate affected by treatments

I have looked at a lot of R datasets, postings in DASL, and elsewhere, and am not finding very many good examples of interesting datasets illustrating analysis of covariance for experimental data. ...
1
vote
1answer
192 views

R - Test for homogeneity of regression slopes results in singular model

I am trying to check the assumptions of a two-way ANCOVA. So in my model I have two factors (F1, F2) one dummy coded two level covariate (C) one dependent variable (D) In order to check the ...
0
votes
0answers
34 views

Seeking covariates that can negate the effect size of treatment groups in an ANCOVA model

I was going to build an ANCOVA model with two treatment groups (climbed/unclimbed) and a set of 10 potential environmental covariates which may collectively remove the significance of the climbing ...
0
votes
1answer
30 views

How is the coefficient of determination in ANCOVA computed?

Given the following ANCOVA model: $Y_{ij}=\mu+\alpha_i+\beta X_{ij}+\epsilon_{ij}$, $e_{ij}\sim N(0,\sigma^2)$ i.i.d., $\alpha_1=0$, $i=1,..., m$, $j=1,..., n$ Given I have already computed ...
0
votes
0answers
17 views

SSCP in analysis of covariance

I want to use analysis of covariance in R. The model is $y_{ij} = \mu + t_i + r_j + b(x_{ij} - \bar{x}) + e_{ij} $ In R it is possible to get Ryy, Tyy, Eyy, SSE as well as b and adjusted treatment ...
0
votes
0answers
28 views

Normalization against Covariates

I have a list of parameters which correlate with 1-2 covariates that I want to control for. Following normalization, I wanted to do comparisons between groups, correlation analysis and probably use ...
0
votes
0answers
30 views

difference between mixed effect and a simple ANCOVA

So I have collected data for 50 years of my dependent variable (continuous) data (x), independent (continuous) variable (y) across 10 locations. My null hypothesis is that the regression slopes ...
0
votes
0answers
33 views

Covariates in Repeated Measures ANOVA

I have made a repeated measures ANOVA which I have two independent variables, three covariates which I will calculate the effects individually for my thesis. I basically conducted two tasks with the ...
0
votes
0answers
283 views

Estimated marginal means and means from descriptive statistics - interpretation in ANCOVA?

I ran an ANCOVA which proved that the covariate is significant. If i understood right, the estimated marginal means show what are the means of the DV when we account for the covariate. Then we could ...
1
vote
0answers
59 views

ANCOVA: Calculate $\omega^2$ for two factorial design

I am trying to calculate the $\omega^2$ effect size for a two factorial (with two levels each) effect size for an ANCOVA with one covariate. Following deliberations from Howell (2012) I got the ...