A situation where the effect of an explanatory variable may depend on the value of another explanatory variable.
1
vote
2answers
909 views
Explanation of “covariate” in general linear model in SPSS
I am completing a project for a client using general linear model (GLM command) in SPSS/PASW (Ver. 17)
Basically, the project is designed to find out if factors such as gender and age affect the ...
1
vote
0answers
264 views
Contrast to ANOVA with interaction term
I need to fit orthogonal contrasts to the following model. The following example data.
...
0
votes
1answer
1k views
How do you plot interaction effects in SAS? [closed]
I want to plot interaction between two variables in SAS. One is continuous and the other is binary.
2
votes
1answer
810 views
Error bars in interaction plot for ANOVA
I notice whenever I see an interaction plot for say a simple two factor ANOVA there are no error bars present, just the points for the estimated means. Is it ever appropriate to display error bars in ...
2
votes
2answers
1k views
Interaction suppresses the main effect? How to interpret it?
I have a simple model without interaction and it stated significant effect for all the explanatory variables (continuous variable rok and categorical variables obdobi (levels hn and nehn) and kraj:
...
1
vote
1answer
398 views
Is it possible to have negative values in a simple slope analysis for dichotomous predictors?
I am currently using the simple slope analysis to examine the significant interaction effects between my continuous moderator and a dichotomous predictor (values 1 & 2)on a continuous DV. I have 2 ...
0
votes
1answer
115 views
Subdividing a dataset
I know I can subdivide a dataset by socio-demographic factors such as gender, age, income level etc. and analyse the responses for each set separately and then compare the results.
For example, I am ...
3
votes
1answer
6k views
How to analyse a moderator effect in hierarchical multiple regression with covariates?
I am trying to find an appropriate method to examine the significant interaction effect in my hierarchial multiple regression analyses.
I am looking at moderation analysis but most of of the methods ...
3
votes
5answers
525 views
Is it appropriate to examine an interaction effect that is almost statistically significant?
I am conducting a 2x2 within-subjects design. When I plot my results it appears that there will be an interaction between my variables but unfortunately none is emerging p=0.08. I find it a shame that ...
0
votes
1answer
97 views
How do you model a scalar response using a scalar IV, a categorical IV and categorical covariate w/ interactions?
So I originally thought I would be able to solve this problem fairly easily with ANCOVA, but now that I've thought more deeply about it I realized it is not so simple.
Essentially we have a scalar ...
3
votes
1answer
581 views
How do I interpret interaction coefficients in a temporally lagged regression model?
I am running a linear regression on daily price returns and I want to capture the interaction between subsequent returns:
$r_{t+1} = \alpha + \beta_1 r_t + \beta_2 r_{t-1} + \beta_3 r_t \cdot r_{t-1} ...
4
votes
1answer
329 views
Representing the anova's interaction in R
I read in the book The basics of S and S-plus that "A:B" functions as "Interaction between A and B".
However, in other book I read "There is never an interaction effect for two factors when one is ...
5
votes
3answers
2k views
Linear regression with factors in R
I'm trying to understand how exactly factors work in R. Let's say I want to run a regression using some sample data in R:
...
1
vote
1answer
338 views
Plotting interaction effect without significant main effects (not about code)
This is not a question about implementation:
I have a GLMER model with a significant three way interaction. Neither of the two way interactions or main effects are significant. I accept this model ...
6
votes
2answers
2k views
How to test whether a regression coefficient is moderated by a grouping variable?
I have a regression done on two groups of the sample based on a moderating variable (say gender). I'm doing a simple test for the moderating effect by checking whether the significance of the ...
5
votes
3answers
491 views
Significance and credibility intervals for interaction term in logistic regression
I fitted a Bayesian logistic regression in WinBugs and it has an interaction term. Something like this:
$$\mathrm{Prob}(y_{i}=1) = \mathrm{logit}^{-1} (a + b_{1}*x_{i} + b_{2}*w_{i} + ...
1
vote
2answers
1k views
Dissecting three-way interactions
I'm trying to interpret a significant three-way interaction. Basically, I've used hierarchical regression to analyse my data, and I have come up with a significant three-way interaction.
My DV is ...
5
votes
1answer
809 views
Coding an interaction between a nominal and a continuous predictor for logistic regression in MATLAB
So our data is structured as follows:
We have $M$ participants, each participant can be categorized into 3 groups (G $\in {A,B,C}$), and for each participant we have $N$ samples of a continuous ...
29
votes
11answers
8k views
Including the interaction but not the main effects in a model
Is it ever valid to include a two-way interaction in a model without including the main effects? What if your hypothesis is only about the interaction, do you still need to include the main effects?
4
votes
2answers
252 views
Why does adding statistically significant interaction reduce true positives?
I am trying to increase my model accuracy by taking into account interaction effect of relevant variables.
I am choosing variables to interact based more on the common sense than on trying every ...
4
votes
3answers
255 views
Counterexample for interaction and parallel curves?
It is said that if the plots of the hypothetical responses are not parallel, but crossed, there is interaction. Suppose we have two factors. Is it possible that the plots cross but we do not have ...
2
votes
1answer
680 views
Power analysis for moderator effect in regression with two continuous predictors
Related to an earlier question on power analysis for multiple regression, a social science researcher asked me about power analysis for moderator regression (i.e., an interaction effect).
The ...
7
votes
2answers
3k views
How to draw an interaction plot with confidence intervals?
My attempts:
I couldn't get confidence intervals in interaction.plot()
and on the other hand plotmeans() from package 'gplot' ...
4
votes
1answer
378 views
Interactions between non-linear predictors
I have data on 70,000 students, nested in 120 schools. I'm starting with fixed effects for the schools, but at some point I might start letting intercepts and slopes vary.
Some key predictors ...
5
votes
1answer
2k views
Which non-parametric test can I use to identify significant interactions of independent variables?
I have an experiment producing results (dependent variables) that don't pass tests of normality, thus I am testing hypotheses using non-parametric tests.
My DVs are continuous, while my factors ...
2
votes
2answers
608 views
Normal distribution necessary to assess moderating and mediating effects?
Is linear regression only suitable for variables with a normal
distribution?
If so, is there an alternative nonparametric test to test mediation or moderation?
4
votes
2answers
2k views
Calculating and interpreting effect sizes for interaction terms
Can an effect size be calculated for an interaction effect in general and more specifically using the F-statistic and its associated degrees of freedom? If yes, should this be done and what is the ...
5
votes
1answer
908 views
Conducting planned comparisons in mixed model using lmer
When deconstructing my mixed effects model, I found a three-way significant interaction. I calculated my p-value by using maximum likelihood ratio tests allowing for a comparison of the fit of the two ...
4
votes
2answers
1k views
3
votes
1answer
841 views
Test for interaction contrasts using Prism or R
Please reference this question (stats.stackexchange.com) http://bit.ly/got8Bs for study design and initial reply from caracal.
My question now is: How can I test for an interaction contrast between ...
5
votes
1answer
716 views
Interaction between ordinal and categorical factor
What analyses can be used to find an interaction effect in a 2-factor design, with one ordinal and one categorical factor, with binary-valued data?
Specifically, are there any types of analyses that ...
2
votes
0answers
318 views
Interactions in Log Transformed DV
I built a fixed effects model using time series cross sectional data. The model was built using PROC MIXED in SAS. There are 2 effect coded attributes in the model and inteactions. One dummy ...
11
votes
3answers
3k views
What if interaction wipes out my direct effects in regression?
In a regression, the interaction term wipes out both related direct effects. Do I drop the interaction or report the outcome? The interaction was not part of the original hypothesis.
9
votes
1answer
3k views
Is interaction possible between two continuous variables?
All of my variables are continuous. There are no levels. Is it possible to even have interaction between the variables?
12
votes
5answers
2k views
What are best practices in identifying interaction effects?
Other than literally testing each possible combination of variable(s) in a model (x1:x2 or x1*x2 ... xn-1 * xn). How do you ...
