Linked Questions

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1answer
2k views

Dropping insignificant interaction term makes insignificant main effect significant: what do? [duplicate]

I have a mixed effects model with one random effect and two fixed effects, both of which are of interest. There is some reason to believe that there would be an interaction between these two fixed ...
2
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3answers
192 views

Is it possible to use linear model $Y=aX_1+b(X_1\times X_2)+c$? [duplicate]

I am doing linear regression with SPSS. There are two potential Predictors $X_1$ and $X_2$ for Dependent Variable $Y$. I found that $X_1$ and $X_2$ are strongly correlated $(r=0.63, p<0.001)$. So I ...
1
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3answers
516 views

Why include insignificant main term when interaction term is included? [duplicate]

Most of the statistics material suggest that when the interaction term is significant, even though the main effect term is not significant, we still keep the main effect term. For example: $$z = a + ...
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0answers
2k views

Is it valid to include several interaction terms but exclude main effects because only interaction effects are significant? [duplicate]

I have a statistical problem in connection to interaction effects and main effects in the social sciences. I am doing a regression where I have two interaction terms with one common variable. The ...
2
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2answers
396 views

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 ...
0
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1answer
304 views

How to report a multiple linear regression equation when the interaction makes lower order items non-significant [duplicate]

I've read a number of the other discussions I can find on here about lower order items and interaction terms in regression but either my statistical incompetence is preventing from seeing it or I ...
0
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2answers
60 views

There are two variables. If they are not significant, can they be interaction items? [duplicate]

If neither x1 nor x2 is significant for y (y=x1+x2 +x3+𝜀). Is it necessary to make the model y = x1 + x2 + x1*x2 + x3 +𝜀? (In fact, the interaction term X1X2 stands out in my analysis.)
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0answers
83 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:...
3
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1answer
42 views

Interaction with dummies [duplicate]

I have a question about econometrics in general. If I have a regression with an interaction between two dummies, do I need to have those dummies separated in the regression too. I have this regression:...
0
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0answers
56 views

Dropping main effect while retaining interaction effect [duplicate]

There has been a lot of discussion on interaction terms on this site but I'm looking at a specific situation: I have 3 groups and a continuous independent variable X;Group1, Group2 are represented by ...
0
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0answers
36 views

Why lower order term is necessary when higher order term is compulsory [duplicate]

I came across a result today stating that if the coefficient of the highest order of independent variable in the regression equation comes out to be necessary (via hypothesis testing), then the lower ...
0
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0answers
18 views

Which way of regression modelling is correct among below options, when the predictor is a product term? [duplicate]

I am modeling a response Y against a predictor X, which is a product of two variables X1 and X2. I am interested in the coefficient of X. Mathematically which way of modeling is correct?: Y ~ X Y ~ ...
67
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18answers
89k views

Statistics interview questions

I am looking for some statistics (and probability, I guess) interview questions, from the most basic through the more advanced. Answers are not necessary (although links to specific questions on this ...
72
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7answers
44k 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....
63
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4answers
62k views

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 ...

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