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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84
votes
17answers
67k 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?
67
votes
7answers
38k views

Do all interactions terms need their individual terms in regression model?

I am actually reviewing a manuscript where the authors compare 5-6 logit regression models with AIC. However, some of the models have interaction terms without including the individual covariate terms....
121
votes
9answers
48k views

Obtaining knowledge from a random forest

Random forests are considered to be black boxes, but recently I was thinking what knowledge can be obtained from a random forest? The most obvious thing is the importance of the variables, in the ...
24
votes
4answers
25k 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.
6
votes
1answer
5k views

Interpretation of interaction term

I have a model: $$ \ln({\rm earnings}) = a+b_1{\rm female}+b_2{\rm white}+b_3{\rm female}\times{\rm white} $$ ${\rm female}$ and ${\rm white}$ are dummy variables. I have interpreted $b_1$ and $b_2$: ...
2
votes
1answer
8k views

Testing for moderation with continuous vs. categorical moderators

I am testing an interaction effect where $X$ and $Y$ are continuous variable and $M$ (Moderator) is a categorical variable (effects coding $+1$, $-1$). I have no clue about how to do a post-hoc ...
23
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3answers
41k views

Interpreting interaction terms in logit regression with categorical variables

I have data from a survey experiment in which respondents were randomly assigned to one of four groups: ...
19
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1answer
36k views

What is the non-parametric equivalent of a two-way ANOVA that can include interactions?

Hi I am trying to find the non-parametric equivalent of a two-way ANOVA (3x4 design) which is capable of including interactions. From my reading in Zar 1984 "Biostatistical analysis" this is possible ...
7
votes
1answer
8k views

Interaction in generalized linear model

I have 2 continuous variables as my predictors and the interaction between them, so 3 effects all together (when I center my predictors only the interaction is significant). I am using a binary logit ...
6
votes
2answers
7k views

In three-way ANOVA, how to interpret the three-way interaction?

I have a significant three-way interaction (with no significant two-way interactions and no significant main effects). To begin with I have followed this up with two two-way ANOVAs (one at each level ...
14
votes
1answer
9k views

Interpreting the regression output from a mixed model when interactions between categorical variables are included

I have a question about my use of a mixed model/lmer. The basic model is this: lmer(DV ~ group * condition + (1|pptid), data= df) Group and condition are both ...
25
votes
3answers
36k views

Why could centering independent variables change the main effects with moderation?

I have a question related to multiple regression and interaction, inspired by this CV thread: Interaction term using centered variables hierarchical regression analysis? What variables should we ...
35
votes
5answers
29k 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 ...
3
votes
2answers
194 views

Can I analyze or model a conditional correlation?

In my research I'm looking at the correlation between self-harm and aggression (both continuous). Now, I also have some variables (e.g. depressive symptoms; also continuous) which I do believe ...
7
votes
1answer
28k views

The main effect will be non-significant if the interaction is significant? [duplicate]

I am using linear mixed models to identify important factors, and it turns out that: A: significant B: not significant ...
12
votes
4answers
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 ...
6
votes
3answers
18k views

How to investigate a 3-way interaction?

There is a significant 3-way interaction in a data-set I'm working with. The interaction involves both categorical and quantitative variables. I have been pointed towards simple slopes and this ...
6
votes
2answers
4k 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 ...
9
votes
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 ...
6
votes
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 ...
2
votes
1answer
139 views

How to code values for males when they're only meaningful for females? [duplicate]

I'm building a predictive model for a medical condition that happens in both men and women. Physicians have reported that in some cases for women, their menstrual history seems to be a risk factor, ...
24
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1answer
16k 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?
20
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5answers
21k views

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 ...
2
votes
1answer
651 views

Investigating interaction

Please I need to check for interaction before building an explanatory model (logistic regression). I have 16 interaction terms in total. Please how what is the best way to go about it. Will I need to ...
7
votes
1answer
3k views

Interpreta​tion of main effect when interactio​n term is significan​t (ex. lme)

As an example I use Pinheiro, J. C. & Bates, D. M. 2000. Mixed-effects models in S and S-PLUS. Springer, New York. page 225. Rats whose body mass has been measured are fed by 3 different diets ...
2
votes
1answer
614 views

ols vs logistic regression, does the interpretation of interaction differs?

My question concerns the interpretation of interaction in ols vs logistic regression. Let us imagine that I have two independent variables, $y_{1}$ is the probability of watching TV at least once a ...
3
votes
1answer
3k views

How to interpret interaction continuous variables in logistic regression?

I am struggling to understand and interpret the interaction term in a logistic regression. The explanatory variables are temperature (categorical), ...
18
votes
3answers
48k views

How to interpret main effects when the interaction effect is not significant?

I ran a Generalized Linear Mixed Model in R and included an interaction effect between two predictors. The interaction was not significant, but the main effects (the two predictors) both were. Now ...
11
votes
3answers
9k views

Joint model with interaction terms vs. separate regressions for a group comparison

After gathering valuable feedback from previous questions and discussions, I have came up with the following question: Suppose that the goal is to detect effect differences across two groups, male vs. ...
5
votes
3answers
15k views

How does the interpretation of main effects in a Two-Way ANOVA change depending on whether the interaction effect is significant?

As far as I can tell this question has never been asked before. There are several questions that touch on related issues, but as far as I can see none of them have provided a definitive answer to this ...
11
votes
2answers
16k views

How can one plot continuous by continuous interactions in ggplot2?

Let's say I have data: ...
9
votes
1answer
15k views

Interpreting coefficients of an interaction between categorical and continuous variable

I have a question about the interpretation of the coefficients of an interaction between continuous and categorical variable. here is my model: ...
8
votes
1answer
7k views

Interaction term using centered variables hierarchical regression analysis? What variables should we center?

I'm running a hierarchical regression analysis and I have some little doubts: Do we calculate the interaction term using the centered variables? Do we have to center ALL the continuous variables we ...
7
votes
1answer
4k views

How do I create and interpret an interaction plot in ggplot2?

I am trying to make an interaction plot for this set of data, but I want to make it with ggplot2. I am trying to predict VP using the predictors G and P, (these are columns in the dataset which I have ...
4
votes
1answer
2k views
9
votes
2answers
14k views

How do you plot an interaction between a factor and a continous covariate?

I would like to plot on the same graph the interaction between my continuous predictor and my categorical moderator. I know how to do it when both are categorical (factor interaction), but don't ...
6
votes
1answer
4k views

How to interpret the significant interaction of two non-significant main predictors?

I have two non-significant main binary variables in my binary logistic regression model, but their interaction is significant. The variables are centered and no multicollinearity is the case (all VIFs ...
5
votes
1answer
534 views

Interpretation of interactions between categorical data

I have data that looks a bit like this ...
3
votes
1answer
5k views

Interpreting a significant 2-way interaction with post-hoc tests

I'm analyzing reaction time data from a repeated measures ANOVA with the following design: Factor 1 (between-group): GROUP (controls, clinical) Factor 2 (within-...
2
votes
3answers
2k views

Does it make sense to interact 2 dummy variables?

I am running a logistic regression, where the dependent variable is marital status. And I assume that educated women are different from women with e.g. high school degree and are less likely to marry. ...
6
votes
1answer
4k views

Cohen's d for 2x2 interaction

I have a significant 2x2 interaction in a between-subjects design. I would normally report omega-squared as my effect-size measure, but I've been asked to provide Cohen's d instead? Can Cohen's d be ...
4
votes
2answers
7k views

Does triple interaction need to include all main effect variables?

I have a triple interaction: AxBxD, where A and B are continuous variables and D is a dummy. My regression is Y = A + B + AxB + AxD + AxBxD In this case, do I HAVE TO include BxD also? In theory here ...
0
votes
1answer
118 views

Prediction using fixed effects in glmm

I have the following generalized linear mixed effects model (mcmcglmm in R) with data based on this paper. Sex is a two level factor (M or F), ...
6
votes
2answers
2k views

Interpretation of multiple logistic regression with interactions in R

I am trying to look at whether 2 variables (one dichotomous categorical and one continuous) predict the occurrence of a dichotomous categorical dependent variable. ...
17
votes
2answers
10k views

Two negative main effects yet positive interaction effect?

I have two main effects, V1 and V2. The effects of V1 and V2 on the response variables are negative. However, for some reason I am getting positive coefficient for the interaction term V1*V2. How can ...
5
votes
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: <...
7
votes
1answer
8k views

How to calculate the standard error of the marginal effects in interactions (robust regression)?

what I am interested in learning is how to calculate the std error of the marginal effects of a X variable when it is part of an interaction, especially in robust regression. There are tipically two ...
9
votes
1answer
10k views

Cox proportional hazard model and interpretation of coefficients when higher case interaction is involved

Here is the summary-output of the Coxph-model I used (I used R and the output is based on the best final model i.e. all significant explanatory variables and their interactions are included): ...
3
votes
3answers
8k views

Interaction term in linear regression

I have two variables, and the relationship between them looks like that in this plot: ggplot(mtcars, aes(wt, mpg)) + geom_point() The relationship between ...
1
vote
3answers
28k views

creating interaction term for dummy variables and categorical variables

I want to create interaction term by using dummy variables and categorical variables. For example, if I want to create interaction term by gender(0=male, 1=female) and education level(0=less than ...