1 vote
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 ...
240 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 vote
624 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 + ...
523 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.)
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 ...
457 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 ...
515 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 ...
73 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:...
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:...
59 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 ...
44 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 ...
19 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 ~ ...
1 vote
14 views

### Linear regression with interaction variables need all interacted variables as independent variables? [duplicate]

Say we have a dependent variable $Y$ and two independent variables $X_1$ and $X_2$. If we are doing the linear regression with interacted variables, do we need to include both $X_1$ and $X_2$ as ...
13 views

### When including an interaction term, do I have to put each variable separately as control variables? [duplicate]

I'm new to econometrics and was wondering when including an interaction term do I have to put each variable separately as control variables? I know this is the case for a difference in differences. <...