Linked Questions

3 votes
1 answer

Can we skip the lower order terms in interactions? [duplicate]

This question is about three-way interaction and the possibility of applying without second lower terms with keeping the main variables in the equation not like the other questions. In fact the other ...
Funn Me's user avatar
  • 39
1 vote
1 answer

Are lower-order interactions a prequisite for three-way interactions in regression analysis? [duplicate]

I'm applying growth curve modelling and am interested in modelling a three-way interaction between predictors A x B x C. From what I remember a condition for modelling three-way interactions in ...
Rasul89's user avatar
  • 153
123 votes
18 answers

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?
Glen's user avatar
  • 6,820
69 votes
4 answers

Does it make sense to add a quadratic term but not the linear term to a model?

I have a (mixed) model in which one of my predictors should a priori only be quadratically related to the predictor (due to the experimental manipulation). Hence, I would like to add only the ...
Henrik's user avatar
  • 14k
16 votes
1 answer

Interactions terms and higher order polynomials

If I were interested in fitting two-way interactions between a linear explanatory variable $a$ and another explanatory variable $b$ that has a quadratic relationship with the dependent variable $y$, ...
Sarah's user avatar
  • 1,237
5 votes
2 answers

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 ...
Steven Gates's user avatar
2 votes
1 answer

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 ...
Rahul's user avatar
  • 81
2 votes
3 answers

Whether to include $x$ and $x^2$ in regression model examining diminishing returns when only $x^2$ is significant?

I have a data set with sales as $Y$ and total retail shelf space ($x$). I want to investigate the diminishing return, i.e. whether additional shelf space would contribute to more sales. I did ...
Tom's user avatar
  • 21
3 votes
3 answers

What is the meaning of the beta for the interaction between continuous variables in a linear mixed-model?

If I create a mixed-effects linear regression model similar to the following (using the lme4 package in R), where all of the fixed effect variables are continuous: ...
Mel's user avatar
  • 213
2 votes
1 answer

Interaction Terms and Logit Models

I have read the previous discussions on interaction effects and main effects, and I have a question on the subject. I am running a destination choice model (multinomial logit), and I have one ...
errorterm's user avatar
2 votes
1 answer

Why lasso yield a higher mse then ridge?

I do a rige and lasso regression on a train data set and get the lambdas via cross validation and evalute the prediction ...
Dima Ku's user avatar
  • 341
5 votes
2 answers

Testing significant differences between regressions in R

I am running several phylogenetic least squares analyses in R, where I'm taking an existing data set for several species, and adding two new species for which I have data. I want to do is test whether ...
Nate's user avatar
  • 51
4 votes
2 answers

Multiple Regression: Two Binary ind. vars. - Can an interaction term be significant, when the main effects are not?

I think this is a simple question, but I'm having difficulty coming up with a test or example for this. Consider lm(A ~ B*C, data=D) where A is continuous; B and C ...
Davis70's user avatar
  • 117
1 vote
1 answer

AIC/BIC vs the rule of "must include lower order interaction"

I am running a series of mixed effect models, which include both linear and quadratic term of a variable T (continuous) and the main IV I (categorical), and facing a dilemma. Model 2 include ...
user6606453's user avatar
2 votes
2 answers

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 ...
Wei's user avatar
  • 23

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