Analysis of Covariance.
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1answer
16 views
Insignificant block effect in two-way block design
I used a two-way ANOVA to analyze data collected in a randomized complete block design:
Y~Treatment+Block, where blocks represented spatial units
Whereas Treatment had a significant effect on Y, ...
0
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1answer
22 views
How do I derive slope and intercept for each group in regression model with a categorical and 2 continuous predictor variables?
$IQ = b_0 + b_1Group + b_2Age + b_3Income + b4\times Group\times Age$
Group is dummy coded ($0,1$)
I assume that the interaction of Group x Age tests the group difference in the slope of the IQ vs. ...
1
vote
1answer
59 views
2x3 ANOVA interaction no longer significant after including a covariate?
My experiment had a 2x3 design with one covariate. If I analyse the results using an ANOVA, I get a strongly significant interaction between the two main factors (p<.001). If I add the covariate ...
-1
votes
0answers
26 views
Why is an ANOVA interaction no longer significant after including a covariate? [duplicate]
I have initially run a 2x2x2 Anova and found some significant interaction between the independent variables. I then ran an ANCOVA where I added a covariant. I am confused with how to interpret the ...
2
votes
1answer
67 views
Why is ANOVA interaction no longer significant after including a covariate?
I have initially run a 2x2x2 Anova and found some significant interaction between the independent variables. I then ran a ANCOVA where I added a covariate. I am confused with how to interpret the ...
-1
votes
0answers
16 views
how to get covariates for these type of data [closed]
i have data on teachers-students responses on the usage of some particular teaching methods, I intend to use ancova for the analysis but don't know how to get the covariates. please advice me?
0
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0answers
64 views
Interpretation of interaction effects for ANCOVA in SPSS
I am now evaluating the results of my experiment on what influences the likelihood of installing a specific application (continuous variable). I manipulated 2 factors: reputation of a provider of the ...
0
votes
0answers
27 views
Incoherent ANCOVA?
I am doing an ANCOVA model in order to explain the gap in a given distance. So I have a control group, and I have several quantitative variables, right now I am trying to evaluate the impact of the ...
0
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0answers
78 views
ANCOVA (GLM) versus Mixed Linear Model with covariate measured at both pre- and post-treatment (in SPSS)
I'm trying to analyze a pre/post study with 4 treatment groups. The Dependent Variable, Speed, measures how quickly a person's facial expression reaches peak intensity; this measure is normally ...
2
votes
0answers
108 views
How to interpret results from non-parametric ANCOVA?
I 'm new to the CV and not very good at statistic:) I would much appreciate some help on a non parametric ANCOVA in R sm package.
I do a pre post analysis on a set of pre/post variables of two groups ...
1
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0answers
55 views
Strange linearity test for ANCOVA
There is an easy way to test the linearity hypothesis for a simple regression model $y \sim {\cal N}(\alpha+\beta x,\sigma^2)$: calling $H_0$ this model, perform a test against the ANOVA model $H_1$ ...
1
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0answers
30 views
Checking for differences in time trends
I have two waterbodies that were sampled for a single water quality variable over time. Both waterbodies were sampled in the fall of each year from 2009-2012. In each year of sampling, 5 replicate ...
2
votes
1answer
99 views
Can ANCOVA disagree with multiple regression?
I have 3 categorical variables (CVa, CVb, CVc) all 0 or 1. Two continuous variables (IV1, IV2) are confounding my observational study. The multiple regression
...
1
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0answers
43 views
Bootstrapping in ANCOVA AND MANOVA in R
I have a difficult one for strong solvers
Can anyone provide us please an example with coding in R of the bootstrapping method in ANCOVA and one in MANOVA
Thank you very much
T
0
votes
1answer
60 views
MANCOVA or several ANCOVAS
I am analyzing pre and post data for which I have 6 DVs for two groups (treatment, no treatment). I want to know if, controlling for pre scores from the 6 measures, post scores differ between the two ...
0
votes
2answers
245 views
How i make an ANCOVA in R
I want to make an ANCOVA analysis of data density per plant epiphytes. At first, I would like to know if there is any difference in plant density between two slopes one N and one S, but I have other ...
0
votes
1answer
98 views
SPSS:While performing ANCOVA, I get a warning: large number of columns may cause integer overflow. How do I resolve this?
SPSS Warning
The large number of columns in the design matrix will cause integer overflow. The large number of columns may be due to too many levels in one or more factors, or to higher-order ...
0
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0answers
63 views
Two-way Ancova in SPSS
Does anybody know the syntax to do an ANCOVA with two IV and one covariate in SPSS?
Best,
Nuria
1
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2answers
93 views
Non-normality and heterogeneity in ANCOVA
I am performing an ANCOVA. My dependent variable is the number of days a student is absent from school. As one can imagine, this variable is not normal, so I performed a log10 transformation. When I ...
0
votes
1answer
53 views
Thoughts on best method for testing for differences in slopes of lines (time series data)?
I have 4 sets of 50 year data (one value per year for each of the 4 different categories)- and would like to test for differences in the slopes of the lines. I think ANCOVA is appropriate- though ...
1
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0answers
74 views
Assumptions of Quade Rank-Based ANCOVA
Spelled out in plain English, what are the assumptions of the Quade (1967) rank-based ANCOVA procedure? It's not written very clearly in the paper. For instance, in regular ANCOVA, I believe the ...
3
votes
2answers
110 views
Significant differences among fit lines - ANCOVA not enough?
I often am in the situation of having data sets consisting of an independent variable, a dependent variable, and a factor with multiple levels - for instance, calibration curves for an instrument ...
1
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0answers
28 views
Ancova: What I can do when assumptions aren't met? [duplicate]
Possible Duplicate:
ANCOVA and its disturbing assumptions
I am testing whether prenatal smoking affects intelligence, while controlling for social economic status. I want to use an ANCOVA ...
0
votes
0answers
69 views
Type of ANCOVA design in R
I have the dataset that contains one continuous measure of plant leafs (PC1 scores of individual leafs), that is dependent variable and three others that I need to use as independant, explanatory. One ...
2
votes
0answers
60 views
mixed ancova or difference scores?
I am puzzled with how I should analyze the following data:
The dependent variable is respiratory sinus arrhythmia, a measure of parasympathetic activity (RSA). I have a $5\times5$ full factorial ...
1
vote
1answer
215 views
Should I use ANCOVA or multiple regression with dummy variables?
I am writing a manuscript using an experimental design which predicts interactions between 1 continuous variable and multiple dichotomous variables, all predicting a continuous variable. As is ...
4
votes
2answers
436 views
ANCOVA and its disturbing assumptions
It is possible to test for interaction in Analysis of Covariance (ANCOVA) between the independent variable and the co-variate, but isn't "the homogeneity of regression slopes" an assumption that ...
2
votes
0answers
279 views
Generalized linear model as non-parametric ANCOVA vs. modern robust methods and non-parametric equivalant of ANCOVA
I am a medical student and I'm a rookie in the field of statistics but I was searching and digging for a long time to do a simple (for most of people involved in the field) analysis all by myself, and ...
1
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0answers
214 views
Comparing model fits or regression coefficients for nonlinear models fitted to different data sets
I have kinetic data measured under several treatments (one experiment per treatment) which can be fitted by several nonlinear two-parameter models, how can I compare whether there there are ...
1
vote
1answer
161 views
How to specify ANCOVA interactions in SPSS?
I'm trying to run ANCOVA in SPSS, with a continuous IV as well as a continuous covariate.
Variable Information:
1 DV: Continuous
2 IVs: 1 Continuous and 1 Categorical
1 Covariate: Continuous
I ...
6
votes
3answers
221 views
Baseline differences in RCT: Which variables (if any) should be included as covariates?
I recently completed a study whereby I randomly assigned participants to one of two treatment groups. I tested participants at baseline, immediately post-intervention, 1 months, and 4 months on a ...
1
vote
0answers
126 views
ANCOVA: How does a covariate give insight when comparing the mean to the adjusted mean?
When comparing the direction and magnitude of the difference between the original means and the adjusted means what does the change say about the covariate?
For example: IV = Grade, DV = Test Score, ...
0
votes
0answers
117 views
How do I test the assumptions of a independent two-way ANCOVA with SPSS?
I really need help in testing these assumptions regarding a two-way ANCOVA with SPSS:
Independent variables orthogonal to the covariates
Covariates must have a homogeneity of regression (or ...
4
votes
1answer
196 views
Different ANCOVA results in R using different functions
before my actual ANCOVA I would like to test whether there is a significant interaction between the IV and the CV as this is one assumption for ANCOVA. I found 3 different ways in R to perform an ...
2
votes
1answer
182 views
ANCOVA to check effect of covariate
I want to check whether a group of patients are significantly different from their control group. However, I also want to check if the p-value is still significant in case a covariate is taken into ...
1
vote
1answer
137 views
Interpretation of intercept in ANCOVA
Consider the below ANCOVA example in which I am trying to predict a continuous varibale y by two variables x (continuous) and ...
25
votes
1answer
416 views
How well can multiple regression really “control for” covariates?
We’re all familiar with observational studies that attempt to establish a causal link between a nonrandomized predictor X and an outcome by including every imaginable potential confounder in a ...
3
votes
1answer
520 views
Nonparametric equivalent of ANCOVA for continuous dependent variables
I have an independent categorical variable ($X$ with two categories, $x_{1}$ and $x_{2}$) and two continuous dependent variables ($y$ and $z$).
Using a Mann Whitney test, I know that $y$ is ...
1
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0answers
52 views
Choosing the best analysis
I need to do a data analysis in R. My data consists of 2 populations of animals that have 2 different types of genomes. The children are always born as twins. I also know the mothers' weight and the ...
0
votes
0answers
197 views
Report coefficients of a factor in a GLM
I have a GLM and my explanatory variables are a factor of 9 levels (X1) and a numeric variable (X2).
If I have to report the formula:
$Y = B_0 + B_1X_1 + B_2X_2$
I have 1 coefficient for the ...
3
votes
1answer
161 views
ANCOVA/ANOVA: Testing different models against each other
I have a dependent variable $Y$, an independent variable $X$, and a categorical independent variable T (which can take 2 levels).
Now I have 4 models:
MI: different slopes, different intercepts
...
3
votes
0answers
76 views
Visual depiction of experimental treatments in (Poisson) ANCOVA?
Goal: I want to visually depict the difference between experimental treatments while controlling for a continuous covariate in Poisson regression.
In my experiment, I am seeking to explain the number ...
6
votes
1answer
536 views
Post hoc test of adjusted means (after ANCOVA)
When doing ANCOVAs, software usually gives both unadjusted means as well as adjusted means. However, the post hoc tests for most statistical programs are limited to unadjusted means. Yet, sometimes, ...
2
votes
0answers
64 views
Is ANCOVA proper for my experiment?
I've got a serious problem when trying to analyse the data of my psychological experiment. Here are the details of the experiment:
In each trial, subjects were presented with lateralized colored ...
0
votes
1answer
138 views
Comparing means - 2 repeated measures variables, controlling for covariate with heterogeneous slope
I have a 2 level repeated measures DV of accuracy, and a covariate of response bias. As response bias increases, accuracy level 1 increases while level 2 decreases. I want to see if there is a ...
1
vote
2answers
151 views
To exclude a main effect that is not of interest in ANCOVA, or not? [duplicate]
Possible Duplicate:
Including the interaction but not the main effects in a model
I have an experimental design with pretest and posttest. Two groups, experimental and control group. I am ...
3
votes
0answers
366 views
How do I estimate a repeated measures ANCOVA in R and SPSS?
I'm currently running a perception experiment:
DV: error (this in degrees- how much an observer was away from the real answer)
IV: the time bin (5 levels) in which the unique stimulus appeared
...
1
vote
1answer
244 views
Interactions with R? ANCOVA in R? I want to see if certain variables affect a dependent variable in R using repeated-measures
I have done an experiment in which the same people have been measured in two conditions, the same room with and without plants. I know they performed significantly better on a reverse digit span task ...
3
votes
0answers
128 views
How to tell if a continuous variable is associated with (treatment) change in another variable over time (one group, time 1, time 2)?
Hypothetical: I have treated a sample for depression and have (continuous) depression scores at intake (Y1) and at the end of treatment (Y2). I am wondering if motivation (X) at the start of therapy ...
4
votes
0answers
71 views
Implementing ANCOVA via residuals
While it is often mis-used, I'd like to provide users of ezANOVA() (from the ez package for R) with the ability to specify covariates for ANCOVA. Since
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