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Questions tagged [interaction]

A situation where the effect of an explanatory variable may depend on the value of another explanatory variable.

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How to visualize an interaction effect from a regression?

I have a regression with a harmonic effect of day of the year, which interacts with other variables. I am not sure how to interpret the coefficients. My model is: ...
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0answers
81 views

Covariate present in a logistic regression model as a effect modifier, but not as main effect [duplicate]

Possible Duplicate: Including the interaction but not the main effects in a model I'm studying logistic regression now. And I have a question: Suppose I have a logistic regression model as below:...
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2answers
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Identification of confounder in a logistic regression model example in “Applied Logistic Regression”

I am reading Hosmer's Applied Logistic Regression, and I am a bit stuck in chapter 3, when taking about interaction and confounders. In page 77, it states the following: Using the estimated ...
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5answers
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What is a block in experimental design?

I have two questions about the notion of block in experimental design : (1) What is the difference between a block and a factor ? (2) I tried to read some books but something is not clear: it seems ...
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2answers
341 views

Is it appropriate to suppress the intercept in a regression graph?

In the event of a non-significant interaction between X and M on Y, is it sound to suppress the intercept in the graph that illustrates the relationship between X and Y (X being significant). The ...
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2answers
1k views

Best method to visualize large interaction between two factors

In a simple experiment I asked participants to make acceptability judgements (9-point Likert scale) when they observed different animated virtual characters. I have two factors: character (7 levels) ...
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2answers
528 views

Graphing versus F-test: contradictory outcome

Following the advice here regarding statistical significance versus substantive meaning of a model, I did a scatterplot with 'fit line at subgroups'. My graph clearly shows that there is an ...
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3answers
697 views

General Linear Model without the main effects

In the post here, a contributor (dmk38) makes an interesting, and may I add a very commonsense observation, that to include or not to include the main effects in an interaction model containing the ...
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2answers
5k views

Interpreting main effect and interaction

I am doing a simple marketing project that has the following types of variables: X1 - continuous (e.g. income) X2 - categorical (e.g. gender) Y - continuous (e.g. number of a product type purchased ...
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1answer
657 views

Two-way ANOVA main effect and interaction query

I have a MINITAB printout I was hoping someone could help me with. My question is- from the table below how do I distinguish between a main effect and an interaction? Study: Three drug treatments ...
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3answers
13k views

Reporting main effects and interaction from ANOVA

When reporting a two way 2 x 3 mixed ANOVA I have recently heard that the interaction effect should only be reported if the two main effects are significant (APA style). Is this correct?
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Different ways to write interaction terms in lm?

I have a question about which is the best way to specify an interaction in a regression model. Consider the following data: ...
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2answers
417 views

Graphing versus further testing interactions

Following the question here, I have come across different (textbook) recommendations. Some authors suggest that the effect of the moderating variable is best understood in a graphic form. Others ...
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19k views

“Moderation” versus “interaction”?

I have come across these two terms which are used interchangeably in many contexts. Basically, a moderator (M) is a factor that impacts on the relationship between X and Y. Moderation analysis is ...
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1answer
594 views

What does “to center two IVs” mean in the context of an interaction?

I am just wondering what does "to center two IVs" mean in the context of understanding an interaction. The IVs are A and gender and the DV is B. Is it necessary for the main effects of a new ...
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2answers
11k views

Significant interaction between covariate and factor in SPSS GLM

In testing gender difference on the relationship between variable A and B, A is the covariate (or independent variable) B is the dependent variable Gender is the factor As I understand it, if there ...
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2answers
6k views

General linear model with interaction term in SPSS

Following my question here, I will be most grateful for further assistance to clear my confusion. The confusion is because I have read in many places that when you use ANCOVA in GLM (in SPSS), the ...
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2answers
7k 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 ...
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3answers
25k views

How to calculate the difference of two slopes?

Is there a method to understand if two lines are (more or less) parallel? I have two lines generated from linear regressions and I would like to understand if they are parallel. In other words, I ...
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0answers
643 views

Contrast to ANOVA with interaction term

I need to fit orthogonal contrasts to the following model. The following example data. ...
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1answer
4k 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.
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1answer
3k 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 ...
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2answers
3k 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: <...
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1answer
1k 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 ...
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1answer
149 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 ...
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1answer
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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 (...
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5answers
2k 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 ...
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1answer
144 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 ...
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1answer
2k 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} ...
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1answer
392 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 ...
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3answers
33k 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: ...
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1answer
525 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 ...
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2answers
6k 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 ...
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3answers
2k 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} + b_{3}*x_{i}*w_{i}...
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2answers
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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 ...
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1answer
3k 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 ...
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17answers
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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?
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2answers
349 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 ...
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3answers
1k 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 ...
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2answers
4k 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 ...
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2answers
33k 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' ...
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1answer
1k 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 (e.g....
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2answers
4k 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 (...
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2answers
4k 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?
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2answers
10k 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 ...
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1answer
2k 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 ...
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2answers
16k views
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1answer
2k 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 ...
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1answer
3k 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 ...
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4answers
24k 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.