Tagged Questions

Analysis of Covariance.

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0
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1answer
9 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
33 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
48 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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0answers
40 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
14 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
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0answers
23 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
8 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
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0answers
9 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
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0answers
17 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
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0answers
20 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
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0answers
42 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
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0answers
28 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, ...
16
votes
4answers
298 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
78 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
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0answers
21 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
20 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
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0answers
12 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
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0answers
21 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
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0answers
19 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
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0answers
23 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
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0answers
88 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
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0answers
50 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 ...
0
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0answers
40 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 ...
1
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0answers
22 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 ...
0
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0answers
37 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 ...
0
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0answers
52 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 ...
0
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1answer
61 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 ...
1
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0answers
53 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 ...
1
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0answers
14 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 ...
0
votes
1answer
22 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). ...
0
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0answers
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 ...
1
vote
0answers
76 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 ...
0
votes
1answer
29 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. ...
0
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0answers
40 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 ...
0
votes
2answers
28 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 ...
2
votes
1answer
76 views

ANCOVA with “Day number” of my study as covariate

I've got some problems with selecting right model/method in my analysis. Two groups of animals (differ by "Treatment") were measured from 1-st to 42-nd day, one common value for each group was ...
0
votes
1answer
253 views

ANCOVA: ordinal covariate on SPSS

I'm trying to run an ANCOVA on SPSS with 3 variables: Gender, score 1, score 2. I want to control for the possibility that gender has an effect the scores, in order to isolate just the relationship ...
0
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0answers
52 views

ANCOVA in R and setting contrasts

Using the following data, I need to determine if, independent of mass, the observed response is associated with sex, location, and/or age ...
0
votes
2answers
31 views

How to code and interpret a regression with 4-level categorical variable and continuous covariates

I have a problem in which 4 groups of people are compared in their performance on a certain test. One way anova shows that they are in fact different. But I also know that my groups are different in ...
0
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0answers
49 views

mixed between-within design when covariate-DV relationship is non-linear (quadratic)

My question is about what method to use for a mixed between-within design when the relationship between the covariate and the DV is non-linear (quadratic). My DV is reasoning task score. There are ...
1
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0answers
137 views

SPSS: How to decompose interactions in repeated measures ANCOVA?

I conducted a study with three categorical within-factors and one continuous personality variable: topic (1,2) x gain loss framing (1,2) x achievement security framing (1,2) x personality I know how ...
2
votes
2answers
135 views

Multiple covariates in an ANCOVA design

I have found a group difference (3 groups) for my dependent variable and now I am supposed to find out if possible covariates influence this finding. What is the best way to "correct" for 5 ...
0
votes
1answer
71 views

What type of test do I use?

I have created 39 question Likert scale survey and want to cross-reference results with 5 demographic questions. I plan on assigning values for each answer 1=strongly disagree, 2=disagree, 3=neutral, ...
2
votes
1answer
76 views

Perform an ANCOVA only if one-way ANOVA proves statistical significance?

I am new to statistics and I have been doing some reading on ANCOVA lately. There is something that is slightly confusing me: When motivating the use of the ANCOVA model, many of the resources that I ...
0
votes
1answer
239 views

paired t test vs linear regression vs ANCOVA

I have data on patients before and after an intervention, half have the treatment, half did not. A paired t-test seems a simple way to determine if there is a significant difference after treatment in ...
0
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0answers
53 views

What happens with covariates when doing contrasts?

I am doing an analysis of covariance (in SPSS) but can't find anywhere how does SPSS treat the covariates when producing the analysis for the special contrasts I specified. Does it take them at their ...
1
vote
1answer
177 views

Repeated Measures ANOVA or ANCOVA?

We recently conducted an repeated measures experiment consisting of two conditions. Each condition consistent of three tasks. The tasks are seen as random factors because they are not comparable among ...
1
vote
0answers
241 views

How to properly analyse longitudinal data from experiments?

I am wondering how one should properly analyse longitudinal data from simple experiments (not observational studies). Imagine an experiment where subjects are first measured at baseline, randomised to ...
0
votes
1answer
68 views

Data formatting for an ANCOVA in SPSS

was wondering if someone could help clarify an ANCOVA for me, or maybe post me in the right direction. I have a set of outcome measures that have been administered pre treatment and post treatment. I ...
1
vote
1answer
70 views

How to test whether the effects of predictors on one DV explains their effects on another in a mixed ANOVA in R

I have data from a psychology experiment in which instructional method was manipulated between subjects via two factors: pretraining (3 levels) and training (2 levels). I assessed participants' ...