Tagged Questions

1
vote
1answer
17 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, ...
1
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1answer
61 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 ...
2
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1answer
71 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
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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
70 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 ...
1
vote
0answers
215 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 ...
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 ...
1
vote
1answer
245 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 ...
0
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0answers
128 views

Interpreting repeated measures ANCOVA in R

I am new to R and trying an analysis that I can't figure out how to do in JMP. I incubated wood samples in various stages of decay at four different temperatures and measured respiration rate and ...
2
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0answers
173 views

Effect of mediating variable independent of effect of possible covariate

Here is a rather involved question. It can be summed up as follows: how can I test the effect of a potential mediating variable, independent of the effect of a possible covariate with which it is ...
2
votes
1answer
464 views

Linear model overfitting due to too many covariates

My study design involves a control and 2 test groups plus some covariates. Each group consists of around 20 observations. In total I look at around 1,000 variables. I created a linear model using the ...
2
votes
1answer
100 views

How to determine if a change in F value when introducing a covariate, is significant?

My question may be very basic but I hope that you can help me. I have got two groups (A and B). I am measuring two continuous biological measures (X and Y) which are significantly positively ...
2
votes
1answer
98 views

Proper order of variables in unbalanced ANOVA

If you have unequal sample sizes in cells, then the order in which you enter model terms changes your results for sequential or Type I SS. The first variable to enter the model is allocated its ...
5
votes
1answer
1k views

Repeated-measures ANCOVA in R?

experts, I would like to ask for advice regarding the analysis of a dataset I am currently working on. In the experiment subjects were tested in a reaction time task (RT as dependent variable). In ...
2
votes
0answers
374 views

Using variations of ANCOVA for non-normal distributions

My first question here, hope to be relevant to the community. Im into CS course and a total rookie on statistics, so let me know if more detail is needed and I will edit the post. I have a problem ...
5
votes
1answer
1k views

How to choose between ANOVA and ANCOVA in a designed experiment?

I am conducting an experiment which has the following: DV: Slice consumption (continuous or could be categorical) IV: Healthy message, unhealthy message, no message (control) (3 groups in which ...
1
vote
0answers
109 views

Interaction terms and BUGS

It occurred to me that how one writes an interaction term in BUGS depends on the types of predictors that are "interacting". Suppose data that are long (rather than wide). Then, a model with an ...
5
votes
1answer
596 views

Should the difference between control and treatment be modelled explicitly or implicitly?

Given the following experimental setup: Multiple samples are taken from a subject and each sample is treated multiple ways (including a control treatment). What is mainly interesting is the ...
4
votes
2answers
449 views

Longitudinal relationship between chocolate consumption and happiness: repeated measures ANOVA?

I am using SPSS and having some trouble with a research question which is analogous to the hypothetical question: Is there a longitudinal Relationship between Happiness and Chocolate Consumption? ...
17
votes
2answers
5k views

Best practice when analysing pre-post treatment-control designs

Imagine the following common design: 100 participants are randomly allocated to either a treatment or a control group the dependent variable is numeric and measured pre- and post- treatment Three ...
14
votes
6answers
1k views

Good resource to understand anova and ancova?

I am running experiments for a paper and am looking for an interesting book/website to understand properly how anova and ancova work. I have a good math background so I don't necessarily need a ...
8
votes
3answers
3k views

Post hoc tests in ANCOVA

Question: What is a good method for conducting post hoc tests of differences between group means after adjusting for the effect of a covariate? Prototypical example: Four groups, 30 participants ...