Analysis of Covariance.

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20 views

How do I statistically test whether two intervention types have significantly different effects in a meta-analysis?

I have the following problem: I am researching the difference in effects (as measured by standarized mean differences (SMD)) of two intervention types. (let's call them intervention 1 and intervention ...
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8 views

Can I use a covariate in a RM-ANOVA design and can the covariate be ordinal?

I'm having some trouble deciding what the best approach is to may data. The following is the setup of the study: Between-subjects factor: Group (2 levels) Within-subjects factors: Time (2 levels), ...
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15 views

Should I include weights in LME?

I have two case studies where I am looking at the influence of a trait (trait A) on mortality (m) of trees and seedlings. Following your comments on ...
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33 views

Anova (missing F statistics), Ancova and mixed modelling on nested dataset

I am performing an analysis in R and wonder how to do it since different methods return very different results. My dataset contains Samples and SubSamples as nested random effects and Type, Dose and ...
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1answer
21 views

ANCOVA - F notation - very simple question

I can't understand the number with the F value ($F_{2, 89} = 0.93, p = 0.09$) in result section from the following paper. Relevant section is quoted below. Can anyone please explain this to me? ...
0
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1answer
26 views

ANCOVA or not? Non continuous covariate

I have done an experiment with an independent and dependent variable. I repeated the experiment 5 times. Obviously all the repeats will be different from one another, some of them significantly so. ...
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35 views

Confused about whether to use t-tests or ANCOVA or ANOVA

I am investing whether vitamin C supplementation can attenuate creatine kinase increases after a strenuous workout. My participants are divided into two groups, VitC group and a Control (no ...
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0answers
14 views

Wild bootstrap in “bordeline" case t-test

I have to compare the mean levels of a continuos variable y (ranging 1-20) subdividing my sample in two groups according to a dichotomous variables (i.e gender). Sample sizes of the two groups are ...
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19 views

Repeated measures ANCOVA

I have a data set with training effects and I measured the outcome variable before, during and after training. This is a repeated measures design and I hope to find an effect of training on the ...
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15 views

Is Wild Bootstrap a good strategy in General Linear Model (ANCOVA) with Assumption Violations (both normal residuals and homoscedasticy)?

I need to perform several GLM's (i.e. ANCOVA’s, with a single continuos dependent variable and several predictors, one dichotomous and some other continuos). I was looking for both a significance on ...
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23 views

Test for ANCOVA validity in R

I have a function Y ~ X + trt; where for each trt (treatment group), I have Y and X which correlate with one another. Basically, I want to use ANCOVA to estimate the model parameters, but I don't ...
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1answer
31 views

Sampling intercept and slope pairs from lm in R

Let's say I have a model Y~X+trt, and by running lm and summary functions in R I get these results: ...
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22 views

How can I make an ANCOVA in R (Prior to a Cox ph model)?

I want to make an ANCOVA analysis of the survival rate of flies after being on a bad diet for the first 21 days of their lives compared to those always on a normal diet. I have studied the responses ...
0
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1answer
38 views

Controlling nuisance covariate in lmer

I want to control for a nuisance covariate in a linear model. Since the covariate interacts significantly with one of the fixed factors, the homogeneity of regression slopes assumption is violated for ...
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23 views

Pairwise comparisons with covariates

I have a simple ANCOVA model such that outcome ~ sex + group with outcome being continuous, ...
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14 views

How should one incorporate multiple forms of information about a single variable into a model?

I sincerely hope this is a question that can be definitively answered! I'll do my best. Let's say I have two treatments, flower removal and defoliation, that are fully crossed in an experiment, and ...
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32 views

Longitudinal pre-post test/follow up

I am an undergrad student trying to get my head around statistical analysis. Can someone help me to make sense of the best way to analyse my data? ANOVA, ANCOVA, t-tests....it is all a foreign ...
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1answer
58 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 ...
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14 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 ...
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35 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 ...
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20 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
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1answer
18 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 ...
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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 ...
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1answer
60 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 ...
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21 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 ...
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45 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. ...
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18 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
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1answer
25 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
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2answers
128 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 ...
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13 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 ...
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18 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 ...
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21 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
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150 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
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2answers
98 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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24 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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30 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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17 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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26 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
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1answer
34 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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1answer
103 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 ...
3
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71 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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21 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
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1answer
35 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
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1answer
32 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
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1answer
13 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
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1answer
107 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
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1answer
67 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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75 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
30 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 ...