Analysis of Covariance.

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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 ...
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42 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 ...
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2answers
15 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 ...
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7 views

Bayesian ANCOVA in R via jags [migrated]

I'm trying to implement a Bayesian ANCOVA that takes account of heteroscedasticity in R using jags. However, despite I've gone through several tutorials of Bayesian simple regression and ANOVA, I ...
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13 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 ...
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32 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 ...
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2answers
24 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 ...
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1answer
39 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, ...
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1answer
53 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 ...
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74 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 ...
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28 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 ...
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1answer
135 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 ...
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39 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 ...
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28 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 ...
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1answer
54 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' ...
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2answers
26 views

Compare regressions among more than 2 groups

I would like to know if there is a way to compare the relationship between a factor (length) and a response variable (lipid content) among multiple groups? I have given up on ANCOVA, as length is ...
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1answer
46 views

Can you put more than one factor in ANCOVA analysis?

I am running ANCOVA on SPSS using post-operation score (continuous) as Dependent variable, pre-operation score (continuous) as Covariate, and 2 groups (categorial 1&0) as Fixed factors. This is ...
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2answers
189 views

ANCOVA in observational studies: what are the assumptions?

Using ANCOVA when groups differ on the covariate is controversial, although Tabachnick and Fidell write that this is a plausible function of ANCOVA in quasi-experimental (or observational) studies. As ...
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1answer
76 views

interpreting ancova and extracting estimated means

Imagine the following data: ds <- data.frame(x=1:10,y=1:10,z=rep(c("A","B"),each=5)) the means for groups in z are: ...
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1answer
59 views

Differences in power in regression versus mean of a ratio

I've been futzing around with the following example, and feel that there must be a good explanation or reference that I am blindly missing. Supposer you have a linear relationship between two ...
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67 views

Can I use ANCOVA for mediation analysis?

I'm a student of psychology and currently drafting the experimental design for my thesis. I could really need some help with the following statistical question. In my experiment, participants will be ...
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25 views

Methodology for finding source of MANCOVA interaction

I am trying to find out the best method for determining the source of a significant MANCOVA interaction. I have 17 traits measured for four locations. Is there an alternate to univariate ANCOVAs ...
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62 views

What is my experimental design?

I am very new to mixed/multilevel models. I have an experiment where we measured 2 scale variables (varA and varB) in 2 different groups of subjects (control and treatment) at 4 different time points. ...
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2answers
113 views

What is the most appropriate test for a multi-year different group/yr experiment?

I've been working on a research project for close to five years now. For my thesis I have to show how "well" did my approach improve things. Setup: Every year we use a tool A to brainstorm and ...
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128 views

How to perform an Ancova with a covariate with nested factors and unbalanced?Is this analysis appropiated?

I'm trying to see differences between years (2008,2009) and between seasons (winter, spring, summer) for a quantitative variable (dependent) in this case is the number of eggs. This variable ...
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1answer
97 views

What is the intuition behind (M)ANCOVA and when/why should one use it?

As per my understanding here's the what/why/when of the following hypotheses tests in a crude sense: t-test: Used when comparing means between two samples ANOVA (one way): Used when you have one ...
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57 views

Several covariates in ANCOVA? Or difference scores?

I am running a quasi-experimental study where I compare changes in brand attitudes across time for four brands, all within subjects. Between Time 1 and time 2, participants see some information and i ...
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36 views

How to interpret results from an experiment where covariate is influenced by the experimental setup?

I am doing study investigating the effect of company's heritage on consumer attitude towards the company/brand. For this purpose I have created two texts: one revealing the history of the company, ...
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49 views

Dependency of a third factor in a correlation between 2 continuous variables?

I'm studying the correlation between 2 continuous variables (A~B), the first is an independent measured variable (A), the second one is a dependent estimated variable (B). I'd like to know i) if the ...
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19 views

comparing location parameters of non-normally distributed variables between groups

Hello I need to compare the mean or median of a continuous but non-normally distributed variable between two groups, but also adjusting for some continuous and categorical covariates. I would think ...
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24 views

ANCOVA with repeated measures IV, violation of slopes

I am running a 2x2x5 mixed factorial ANCOVA, with one within-groups variable, and two between groups variable. I want to check for violation of homogeneity of regression slopes. My covatiate does not ...
3
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1answer
50 views

ANCOVA with repeating covariate

I wonder if someone can help me with an ANCOVA covariate question? Perhaps you may know the answer to my problem. Subjects were assigned to a treatment or control group, and I measured a (continuous) ...
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1answer
73 views

Including a baseline measure of the DV as a covariate in an ANCOVA

I have 4 groups based on BPD symptoms at baseline and follow-up. (BPD T1 and T2; BPD T1 not T2; no BPD T1 but BPD T2; Never BPD). I am examining whether psychosocial functioning outcomes (SOFAS score) ...
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2answers
778 views

What is the difference between “factors” and “covariate” in terms of ANOVA? [duplicate]

I am a bit confused on the term "covariate". It seems like the term can mean two different things. In ANCOVA, the term is used for the third variable that is not directly related to the experiment. ...
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109 views

How do we test the assumption of homogeneity of regression slope in a mixed model ANCOVA

I have a mixed 3x2x2x2 ANCOVA design. The first factor is an within subject factor, 3 types of feedback. The other 3 factors are all between subject:sex, age, feedback source. There is still one ...
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1answer
138 views

Best way to specify a mixed ANCOVA in R?

After using ezANOVA as my primary way of specifying mixed ANOVAs, I've hit a stumbling block when it come to adding a covariate to the model. I am using an ANCOVA ...
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53 views

Parameter Estimates

I have copied my Parameter estimates table below and am not sure how to interpret it or what it means. Any help would be greatly appreciated! Warmly, Carolynn Dependent Variable Parameter B Std. ...
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1answer
485 views

How to test if two regression models are significantly different in R

Generally speaking I want to find out if the regression models I built are significantly different from each other. I have monthly energy consumption data (the independent variable) from a couple of ...
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99 views

Alternatives to ANCOVA when assumptions are violated

I am doing research on organisational change and looking at how certain types of change (e.g. closures of offices, layoffs, investment on activities/functions) have affected seven psychological ...
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15 views

how can I determine the effect of pre treatment on post treatment? [duplicate]

I have two group male and female and I am looking in to pre and post value and I want to determine: 1. the gender effect on improvement (post-pre) 2. the initial value(pre) effect on post value.
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31 views

Biased distribution of covariate levels among batches

I am investigating the physiologic response (gene expression) of two groups of individuals (Group A and Group B) on a continuous environmental covariate in two different environments (E1 and E2). As I ...
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3answers
1k views

Should covariates that are not statistically significant be 'kept in' when creating a model?

I have several covariates in my calculation for a model, and not all of them are statistically significant. Should I remove those that are not? This question discusses the phenomenon, but does not ...
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3answers
132 views

Compare 2 regression lines in R

I have the following data frame ...
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1answer
56 views

Controlling for baseline imbalance

I have a quick question about growth curve modelling and baseline imbalance: do growth curve models control for baseline imbalance and if so, do they control for imbalance in a reliable way, i.e., ...
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2answers
117 views

Robust ANCOVA literature

I am looking for some source of information, some articles about Robust ANCOVA. Can you suggest me something? And do you know any source that directly gives information about how to perform various ...
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1answer
97 views

How to interpret interaction between 2 independent variables with ANCOVA?

I'm measuring the influence of the use of male gaze and nudity in magazines to see if girls self-objectify or not. Now, I want to determine the influence of age. ...
3
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1answer
141 views

Correcting for multiple comparisons on planned contrasts with an ANCOVA

I have done an experiment with 7 treatment conditions designed to reduce alcohol intake, and a control condition. The dependent variable is alcohol intake after treatment, and I have run an ANCOVA ...
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121 views

Is it possible for my mixed model results to be the same as those for a repeated measures ANCOVA? Why don't I get the same results? SPSS

The experiment: Two groups of children perform tasks with three levels of difficulty at two different time points and brain activity is measured. All of the children perform all of the tasks and do so ...
3
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1answer
181 views

Can covariates be categorial variables?

I have a 2x2 experimental design. In the experiment, I also collected the participants' professional qualifications (categorical variable- yes /no). I would like to test the effect of controlling this ...
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128 views

What are the assumptions for repeated-measures MANCOVA?

Are these assumptions correct and the list complete for repeated-measures MANCOVA? sphericity multivariate normality homogeneity of variance homogeneity of covariance matrices homogeneity of ...