Analysis of Covariance.

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7 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 ...
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17 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 ...
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2answers
51 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 ...
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10 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 ...
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12 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 ...
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12 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, ...
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11 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 ...
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1answer
14 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 ...
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29 views

Repeated measures with time varying covariates in R

On this page (Model 5, http://www.ats.ucla.edu/stat/spss/faq/repeat_covar.htm), there is a description of how to carry out this type of analysis using SPSS. Does anyone know how to do the same thing ...
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1answer
22 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 ...
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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 ...
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43 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 ...
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12 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 ...
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1answer
24 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 ...
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1answer
19 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 ...
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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 ...
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1answer
68 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 ...
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1answer
57 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 ...
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65 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 ...
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1answer
20 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 ...
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44 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 ...
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1answer
10 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 ...
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10 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?
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25 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 ...
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25 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?
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56 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 ...
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39 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, ...
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316 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. ...
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1answer
127 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 ...
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27 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 ...
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1answer
23 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 ...
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14 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 ...
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25 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 ...
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25 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 ...
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28 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 ...
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218 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 ...
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53 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 ...
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48 views

ANCOVA in R with unequal sample sizes

I'm trying to assess the outcome of an RCT using R. Participants were randomly assigned to complete one of two online interventions for depression. I want to see if there is a difference in the ...
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25 views

testing for the difference in slopes if independent data is correlated

So I am looking at whether the effect of rainfall on crop yield for 8 different States is similar across these States i.e. I am testing whether the slopes between rainfall and yield is significantly ...
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45 views

R: What is the difference between ANCOVA and drop1?

In one of the slides of a statistics course that I followed the following about using drop1 or ANCOVA is stated. Using drop1 the p-values shown are p-values for deleting one variable at a time ...
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62 views

ANOVA, unbalanced designs, missing data, and multiple comparisons

I am having several problems with my dataset and how best to analyze it. I have measured a series of plant phenology characteristics (with a seperate model for each one - I do not want to combine them ...
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1answer
77 views

Which Statistical Technique (ANCOVA or Taguchi methods) for this problem?

I have one qualitative factor (Treatments) and two uncontrollable factors, temperature and moisture, with one response variable. I'm confused whether I should use ANCOVA with temperature and moisture ...
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56 views

Comparison of t-value and F-value

I have conducted a t-test via SPSS, followed by an ANCOVA (Analysis of Covariance). Now I am wondering if it is correct to report the t-value and then the F-value of the ANCOVA. But are those two ...
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15 views

Scale of control variable in ANCOVA

I am new to the field of ANCOVAs. I want to check if two groups differ in three quantitative variables. At the same time I would like to control for gender and diagnose (6 categories). Is it ...
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1answer
23 views

ANCOVA with complicated research design

I am having a few problems with my analysis and hope that somebody can help me out. About my design: I have 120 respondents, who I showed each 7 facebook posts out of a pool of 16 (randomly assigned). ...
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45 views

Help with a stats question (what analysis to use?)

A common design in research is a study which employs both a treatment and control group with each group being measured at pre-test and post-test. There are many ways to analyze this data to determine ...
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130 views

R: Post hoc tests in ANCOVA with factorial design

Does anyone know how to do post hoc tests in ANCOVA with a factorial design? I have two vectors consisting of 23 baseline values (covariate) and 23 values after treatment (independent variable) and I ...
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1answer
30 views

Odd result for intercept in ANCOVA

I try to perform an ANCOVA for data with two factors and one covariate. The first factor has 2 levels and the second has 4. ...
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52 views

How to report ANOVA F-values when they are zero?

I conducted an ANOVA and one of the F-values for a main effect is .000 on SPSS, and the other is .003 on SPSS. As I am rounding to two decimal places, how do I report these? Does F = 0.00, or is F ...
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2answers
48 views

Linear correlation in ANCOVA - necessary?

I've been told by my stats prof that running an ANCOVA relies on a series of assumptions, including that the the dependent variable and the covariate are linearly related. So, in SPSS the first thing ...